Really intrigued by this game. Very interesting premise and a refreshingly different take on the classic big-dicked son fucks mom and sis...
Warning, spoiler down below:
One thing I'm curious to see is how the relationship between the women will play out. So far, I'm interpreting it as mom being quite angrily jealous at sister for sucking the MC:s cock (other explanations for her anger don't fit, she knows the MC probably wouldn't mind, so being angry at sister for molesting him don't make much sense, and she clearly enjoys pleasuring her son, so the anger can't be because she feels she's been tricked into doing something she really didn't want to do). Together with sisters volatile temper (imagine her finding out mom has ben jerking and sucking the MC:s cock) and the new girl presenting a possible threat to the little family unit, I see potential for some rather aggravated strife and conflict between the women as the story progresses.
But it's also rather heavily implied that the mother might have bisexual tendancies, and both sister as well as new girl are bisexual, so I wouldn't be surprised if going the harem route quite quickly develop into a happy-go-lucky thing where everyone has sex with everybody. This is after all the more common way for things to go in games with a harem-style approach.
Personally, I would actually far more prefer if there's at least one, or several pathways where things instead turn increasingly hostile between the women as their rivalry for the MC:s attention dawns upon them (especially since they, at least mother and sister, probably for the longest of time will try to pretend that they don't have a sexual interest, let alone a romantic interest, in the MC). As it's setup, neither woman have any real grounds for demanding fidellity from the MC (so far, it's just about controlling and containing urges and instincts), which could lead them to take out their jealousy as increased hostility towards each other instead.
Maybe a successful harem build in such a pathway would be for the women to accept that the MC fucks them all, despite the rivalry. There's much interesting that can be done in such a relationship. Take for instance mother teaching and showing daughter how to give head by violently forcing sister down on the MC:s cock and purposefully gagging her with it...