What a bummer!
I loved, loved, loved, No more Secrets and decided to treat myself and wait a bit before starting this one.
As a married man, with children (Ok only boys, so maybe that is different), and with a mother and sisters. I do not understand the guilt of playing an incest game. I never wanted to have sex with any of my relations, but the fantasy taboo in the game itself is just that, a fantasy.
I have no sexual attraction to my RL sisters (not even secretly) that I love dearly, but it is just a convenient plot point for an adult game to have 3 LI in the same household. The dynamic between the characters is already established. Older sibling will be disinterested or bully the MC (Like in RL regardless of gender). Younger sibling will have slight hero worship (Like in RL regardless of gender). And a mother will love you unconditionally. It is the perfect setup that you have without even writing a single word. (And then some developers still fuck it up

)
BTW I feel the same with teenage kids in games. I do not mind if the in-game LI is 15 or 16, but in RL I feel very strong that girls should wait until they are 18. They are not emotionally mature enough to be in a sexual relation with an older man, before they leave high school.
Having said all that, I also believe you should do what is best for yourself, and if quitting the game is that for you, then you should do it. The best of luck to the developer! Enjoy your family!
PS. As someone that have not played this game yet. Can you recommend that I play this game in the current state? Are there a million loose ends? (As a reference, BB is officially abandoned, but it actually stopped at a very satisfactory point)