@Faerin You do you man. And just do your story as you need to. I think you will get the support you need no matter what.
Personally I think making the changes mentioned by
@DrSmith and just allow the player to name the characters whatever they want (Diane, Angela, Mom, Mother, whatever.) But honestly, as good as you have done so far in the story telling and game development, I trust that whatever you decide will be good.
Then again, I am one of the (seemingly few) on this site for whom incest doesn't make or break a game for me. It is neither a turn on or a turn off in my book and as long as the story is well written, the characters attractive, and the gameplay decent then I am happy.