Difficult question to answer, first though, are you intending to have a Harem for this? Its not that appealing that there are already established relationships in the game prior with their involvement with the MC (i.e. Mia and Nicole). As for me, after knowing the implications of what's happening between the two of them (the allusion when they're calling each other before, not yet the lesbian sex itself), my immediate reaction is then to just ignore them outright.
When there's already an established relationship, I just don't bother trying to add them in the harem. I just leave them out to do their own thing. When they're not involved with each other however (meaning both Mia and Nicole are simply friends since they broke up with their husbands), then lesbian interactions (e.g. some light kissing, fingering, touching, etc.) whilst in a threesome becomes fine to me. Take note that I mean is that these things only happens while they're involve with the MC (again, in a threesome for example), outside that they're just normal friends that just so happen to be enamored and together they seduced a guy because of how long they'd been wanting that touch (I prefer the really sweet interactions of Harem members, treating each other like Sisters that just so happen to like/love/want the same guy). The MC must be the focus, to me this just looks like that both Mia and Nicole want a boytoy (a sex friend perhaps, nothing more). They want the MC to be involved with their circle, instead of the other way around where the MC takes both of them in his harem.
If the MC is inside the circle of Mia and Nicole, options for making the other girls of the MC may also get them involved with the unwanted stuff as well. Its not really good to just say that every girl in a Harem should be bisexual, they're may be touching some of the other girls in a threesome but that doesn't mean they are bisexual. Maybe they just want to make it even more hot and rile up the MC.
Moreover, I don't like options that completely remove stuff for those that may want or not want that. I'd rather prefer the dev have an actual final verdict whether to completely remove the unwanted stuff (i.e. Lesbian, Femdom, etc. and some others mentioned above) or to just stick with skippable stuff. Meaning, you just outright remove them from the game altogether.
What I just said in the previous paragraph would be the ideal outcome. This request however, is a bit ridiculous to consider, there may be cases that the game is not on its early stages anymore for a change like this to happen or implemented. In this case, we just gotta' shrug at the compromise where the the Player is given the option at the beginning of the game, to saying yes or no on things they may or may not like.
I mentioned the Femdom and Lesbian tags, but I think I structured this post to also apply on other things that can definitely be avoided. I can probably say more but I may have forgotten some stuff to consider. Lastly, please do see the difference between Polyamory and what a Harem is for your future plans.