I've played so many incest games and I really like them, but I can't see it working in this story, it's so forced that it doesn't make sense to me.
The MC is someone who has been abused and developed trust issues, so I don't see a problem with a counselor caring about this kid, to the point of offering him a place to stay with probably the only person he trusted, the counselor, this shows that she really cared about the kid and wanted to make sure he would be okay; I have some relatives who did something very similar to children in similar situations, so I understand.
Regarding Judy's husband and Hailey and Mia's father, we heard that he hated MC and was overjoyed when he heard MC had died, and I think the person they were talking about was MC's sister, it is very likely that Judy's husband left her, Hailey and Mia, to be with MC's sister, considering that they have something in common which is not liking MC at all, it is unlikely that Judy, Hailey and Mia would continue with him considering how much they like MC.
We hear more from MC's sister than his mother, and we know about his parents' marriage and how they raised their children, so it wouldn't be the mother, so that leaves only the sister or someone who hasn't been mentioned yet.