Hi and welcome! I just want to say I am sorry you have had to go through, what sounds like, a lot of extremely distressing and difficult situations 
You must be a fantastic mom to have raised such a determined kid!
There is no clear answer to his chances on acceptances or FA. I do think schools genuinely want diversity of backgrounds and experiences, and that can be advantageous. Overall any kids chances are going to related to the school admissions rate overall - some are in single digits, some far far higher!
This is thread that may be helpful too: Here are your chances for boarding schools
Luckily decisions are only 2 weeks away. The waiting is sooooooo hard!