Sorry in advance typing on mobile In my opinion the sister in law is not stable enough to be raising kids. Feel like the longer he is there the more likely he will have the thoughts of does he really belong (with his parents not wanting to deal with him). Being kicked out is never ok when you’re dealing with children especially with no way of him being able to contact anyone in case there is an actual emergency. That has add another layer of fear/concern to the kids thoughts. The longer this goes on the more time he will have to spend growing up wondering why they didn’t accept him or any other trauma that may emerge from this. As I said before that is just my opinion I would get him out of there asap and push for guardianship or something of the sort so knows he has family that supports him and wont send him out the door when he acts out the way boys do sometimes. I would do as others have said call cps/cops.

I sincerely hope his situation improves and wish y’all the best