(Edit: I feel like I should clarify, these are the only LGBT characters in the story, and the only characters whose sexualities are even touched on, and they are part of a larger group of people, about 300. This story occurs in America near a large city, so the racial makeup of this group is very mixed.)

(I've asked quite a few other questions about this story, lol.)

In my post-apocalyptic story, my MC, Eris, is Latina and queer, and her love interest, Caspian, is bisexual and adopted by a black lesbian named Ezrith (who was in love with his biological mother). Caspian is romantically interested in Leo, a Latino gay man who is in a relationship with Alexander, an Asian gay transgender man. This is my main cast, and they're pretty much a mixed bag of everything you could imagine.

I've written them to be as diverse as possible without forcing it. For example, I don't focus on the fact that Leo isn't white; I simply state in passing that he has dark skin and a lilting accent. I don't explicitly state that Caspian isn't straight, it's just to be inferred through his behavior around attractive male and female characters. I don't have neon signs screaming, "Ezrith is lesbian," I just have Caspian explain to Eris that Ezrith was in love with his biological mom.

I know minority representation is a good thing, and I'm not white or straight so I usually make an effort to incorporate minorities into my writing that aren't stereotypical. But is there such a thing as having a story that is "too diverse"? Is it unrealistic to have such a diverse cast of characters? Is it alienating to readers who are white and straight to be put into the shoes of someone who is drastically dissimilar to them?

The short answer is, there is no such thing as too much diversity!

Especially when authorship comes from the community being portrayed. So many times mainstream (i.e., white) writers/producers/publishers will look at diversity in terms of matching percentages. So if black people make up 12% of the US population, then make 1 in every 8 characters black (mostly in the background, and lower that percentage because what they really want is what they see in mostly white spaces). Other times, a creative team will include one of everything (from a short list) and pat themselves on the back.

But when non-mainstream characters are dropped in like chocolate chips in cookie batter, you don't really see them. Real diversity is about communities and cultures, not individuals. Sure, keep the individuals, but don't stop there.

When writers of color make their whole world look like them (or at least as the majority), something magical happens. Temper, Afar (comic), Kintu, The Hummingbird's Daughter (all these have a fantasy theme). Other stories are set within minority communities in a white country or are about another country, or set within non-mainstream communities that live in a straight and otherwise mainstream location.

The long answer is, sometimes authors try too hard.

Sometimes you want to highlight a particular community and that's totally cool. Other times you're trying to set a work within a larger community and you find yourself highlighting diversity in a way that overshadows the larger story.

I'll give an example from my own novel. 18 kids from the US time travel to ancient Egypt just before the start of the Exodus. Race and ethnicity is a huge part of my book. Those ancient Jews were not white and a lot of them were of mixed ethnicity. Plus there were a ton of converts from all sorts of backgrounds. My main character and her brother are 100% European Jewish. All the other kids are 1/2 or 1/4 Jewish.

My top characters include a brother and sister who are half black and half Jewish. I also had one sibling group that was part Mexican and another sibling group that was part Native American (they're from Arizona where both those groups are common). This added up to 9 kids who were in part not-white. Half of the total.

If I was just writing about these kids I might have left it as is. The problem is that it was important to my story to have the mostly-European travelers contrast with the Northern African/Middle-Eastern locals they hung out with. So I made the 1/2 Hispanic kids 1/4 Native American instead and made the formally 1/2 Native American kids 1/2 white (non-Jewish European). Now it's 5 kids with a non-European ethnicity.

I still have plenty of ethnic diversity to work with. Because it's mostly with the ancient Hebrews, it works even better to teach the travelers how to overcome their American ideas of who counts as a Jew and how race intersects. I couldn't have done that as well had half the kids been of color.

Gender, sex, and sexuality.

I struggled as well with lavender representation in my story. As I belong to this community myself, I have no desire to write a book where everyone's assumed to be straight. On the other hand, it's an upper middle grade novel. The oldest main characters are 14 (8th grade) and none of them are dating (yes I know sometimes kids that age do date, but mine haven't started yet).

The ancient Hebrew group has marriages and family units around traditional gender expectations. People weren't any less likely to be queer back then (you don't get a ton of rules against something that isn't happening), but it manifested in ways other than family structure. But since I'm focusing on kids (my MC is 12) and writing for kids (upper middle grade is about 8-12 years). And since I want to concentrate on issues of faith and ethnicity, I'm downplaying it all.

I'd be lying if I said I had no mixed feelings, but I am okay about it because it works for this story. If I told the story from the point of view of an older teen or an adult, I might showcase some very different things.

Just because I choose not to tell their stories doesn't erase their existence.

Duh, of course some of my characters are lavender. I didn't sit and try to figure out who; I asked them. (Yes, I'm in the stage where my characters tell me who they are.) Of those 18 kids, 2 grow up to be gay. One is 2 at the time of the story and the other is 14. The 14 year old is my favorite character because he's very complicated (and a total jerk). I show him with his husband and son in the epilogue when they're all grown up. Otherwise, it's not stated in the story. But is it there? Of course! I know what's in his head. I see how his eyes linger on certain young men. I feel his heart beat out of his chest when he's with his new best friend who is from Egypt. Readers who look for it will see it too.

So what about your story?

If it works for you as an author and it works for your story, then have them be who they are now. If it feels forced to you, then make some changes. Next, ask some beta readers or a writing group what they think. I did this with my spouse, whose comic book series just published its second issue (of 20). That story is an explosion of diversity of every kind. So when he told me he thought my US kids should be more European (for the reasons I stated above), I trusted that.

Will you alienate some straight white readers with your story? Yes. Yes, you will.

But every story alienates someone. I posted a couple questions about my story over on Worldbuilding and was shocked at the things that caused people to hate my story without ever having read it. My older kids weren't adult enough; they should take on adult responsibilities. My older kids were snot-nosed brats who couldn't possibly be helpful in any way. My MC couldn't be a leader because she was a girl. And so on.

And ya know what? It's okay. You can't make your story right for everyone. Make it true to yourself and make it publishable.

If you're honest with yourself and find that you're adding diversity in a way that doesn't work for your story, take it out.

If you find you're taking away diversity in order to appease imaginary readers, put it back in.

Find your balance and tell your story.

I don't think it's alienating, but it does press my suspension of disbelief a bit to have such a large fraction of the cast be LGBT characters. Gays are something like 3-5% of the population, with the rest of the letters being an even smaller fraction. Having a group of four LGBT characters with no heterosexual ones is unrealistic unless they are together because they are LGBT. Admittedly, a post-apocalyptic society would be fairly Malthusian and thus likely to put a large emphasis on reproduction, meaning them being outcasts for being LGBT is quite reasonable. So if something like this is part of their backstory, then that's totally fine. But if they're a group of survivors that just happen to fill in the acronym I'm going to be rolling my eyes.

The skin color thing would depend on where the story is set. For example, in post-apocalyptic America, just about any racial makeup is perfectly reasonable. Post-apocalyptic China or Russia, I'd be scratching my head as to where this diversity is coming from.

After the OP's edit, 4/300 characters is not "too diverse". That ratio nullifies all the answers here.

In the age of Star Wars and Guardians of the Galaxy, it's probably not possible to be "too diverse", but robots and raccoons do not represent real people even when writers give them preach-y slogans. There's a big difference between multi-culti window-dressing and attempting to realistically portray oppressed people.

what could go wrong

1. 
   Superficial diversity – watch out for diversity checkboxes, like rolling dice to create an RPG character. You already have some of this going on, so the thing to keep in mind is how their diversity might lead to disagreements and incompatible perspectives. You don't want to have the superficial diversity of ethnic/gender/orientation checkboxes, meanwhile all characters speak and act like middleclass college students from a hip town.


2. 
   Captain Planet – Each represents a monotype or stereotype of accents and heritage foods that doesn't really make sense unless they are cultural ambassadors. In your case this might include ethnic cues and cultural signals when the immediate team would adopt similar speech patterns and phrases among themselves. It might also be spread so thinly among all characters, that it becomes decoration rather than character or worldbuilding. A graphic novel can show ethnic diversity in an instant, but in a written narrative you'll have to put it all in the text.


3. 
   They never interact with "their own" – this one comes from Samuel R. Delany, whose template for writing believable female characters says they need to have meaningful friendships with other women. I've also seen Black authors rant about the token Black character who has no other Black friends or family. Extrapolating to LGBT, it may require the spirit rather than the letter of the rule. The idea is to anchor the characters to close friends outside their role on the team. They should have close friends and surrogate families, past relationships, old roommates. No one hatched from an egg yesterday. The other issue is the characters represent their entire [group] if the story doesn't include others who are in that same [group] who act independently of each other.


4. 
   Unintended hierarchies and biases – minority groups have internal minority groups. In your example you have chosen to make your trans character
   also gay. While that does happen, trans people and their straight
   partners are already erased from "LGBT" organizations and your story seems to
   confirm that bias. Teams also have "leaders" and stories have "lead characters", their importance in the narrative (both diagetically and non-diagetically) can defeat the intent. A problem example is a Black female administer/boss/captain. Diagetically, she is an authority in-world, but non-diagetically she is just a foil or supporting character who is to be ignored or disobeyed by the MC. The unintended message is that diversity is allowed only when it conforms to a bias.

Mary Sue stops the holocaust

It's ok to write a fantasy adventure about people you wish you knew in real life. If it feels like a Mary Sue team-up it probably is, but not every story is character-driven. Sometimes it's about the adventure itself and you want friendly faces to join you. Characters will wear "hats" that let us know when they are good or evil, and villains will be melodramatic and underestimate the team. Things will explode. There will be traveling from A to B, and swashbuckling.

Needless to say, that is a different story than the gravitas you've put into some of your other questions. You might have a dissonance between the characters you want to be friends with, and the characters who prevail in a hellish environment. You will need to destroy those characters to achieve what you want. They will have uncomfortable edges and complications to match that universe. The reader will love and hate these characters. They will do unforgivable things to survive. That's the only way to tell that kind of story.

Mary Sue and the holocaust don't mix.

When I read people say "and then I put the book down because it was preaching at me…", what I think has happened is a dissonance between Mary Sue heroes and holocaust conflicts. The reader is rolling their eyes and wondering when it gets back to the plot rather than a flattering ego-projection.

In 1984 the forbidden romance is hetero, but it wouldn't be significantly different if it was 2 men in a prison camp. The relationship is ugly and brutal, like the world. Readers accept the relationship as integral to the story and the MC's shrinking world, no one would ever accuse it of being "escapist fluff" or preachy. It's just as messed up as the rest of the story.

At the other extreme, Flash Gordon, Captain Kirk, and Barbarella are space thots from an alternate swinger's universe. Slave collars, booty shorts, nymphos and sadists are as ubiquitous as ray guns, but sexy times are all part of the fun. This isn't the story to deliver a sermon about oppression (when they do it isn't terribly deep, it's more rah-rah ego-projection).

Is there middle ground since these story-types are probably incompatible? Sure, every story navigates between authenticity and fantasy, but rarely are they both at the same time.

To achieve your diversity-only LGBT team in an apocalypse where most people have died, they are either thrown together for some reason – like escaping from a concentration camp – or there is healthy suspension of disbelief in order to have the team-up you want – like they meet in a bar on Tatooine and then join the rebels. It's unlikely you can tone shift between "empowering" adventure characters, and genocidal oppression without knocking readers out of the story.