Adding my two cents here! I thought about this a lot before starting to write the game I'm currently developing, and my conclusion is:
It’s all about how you do it.
My game is also a harem game, and when creating the LIs, their personalities, and roles in the world, it just made sense that some of them would be bisexual or at least bicurious. It wasn’t something I tried to force in, it just fits their place in the story.
Personally, I'm neutral on lesbian content, and sometimes enjoy it when it's done right. So I'd make sure that any lesbian content in my game
serves a purpose rather than just being a fetish. It needs to feel natural. Before thinking about the lesbian sex itself, I thought of how I'm presenting the bisexual/lesbian characters to the players. What are their traits? Their role? Their struggles? The goal should be to make the player care about them first. (Unless your game is a fuckfest where players just skip to the sex, in that case romance doesn't matter. lol)
That said, one important thing to keep in mind is that harem players usually see themselves as the MC, since the story is told from their point of view. If two or more LIs are having fun without them, it can feel like they don’t matter there. Because of that, I personally would only include lesbian content during threesomes or group scenes where the MC
IS the focus. (Since your game will have multiple MCs, that might be harder to achieve.)
Here's an example for a subplot in my game:
- The MC needs the help of LI(A) and LI(B) to overcome a problem.
- Both LIs are bisexual but also rivals. They each try to pull the MC to their side, but eventually, they realize they need to work together.
- Through their fights (and with the MC’s involvement), they start to open up to each other and maybe even develop attraction.
- After solving the problem, it will lead to a threesome scene.
But again, it's just how I believe lesbian content should be done in a harem AVN. I'm just developing my first actual project, so I guess we'll see if people like that approach or not.