What a scumbag is the uncle of the MC. He fucks someone while he was married, since the kid was younger than his daughter, then brings the kid in the their family house ( which would be something shameful for his wife at that time) and doesn't look even apologetic while his wife and daughter are clearly suffering.
Honestly, I don't think is right for the mother to abuse the kid and I wish their relationship could be better. But, man, I also would be so pissed in this situation. Sad that divorce wasn't an option in there.
Hope that the MC can help solve and improve his situation.