I am so sorry to hear about your son, OP. You definitely need professional guidance to help you make the best decisions for you and your son. I hope he can stay in the residential program for a good length of time. Assuming you live in the DC area, I suggest contacting The Ross Center --
https://www.rosscenter.com/how-we-treat/dialectical-behavior-therapy. They have wonderful clinicians and a treatment program for teenagers with serious conditions. They also have clinicians that can help you keep your sanity, which is just as important. Hopefully the residential program can also give you some expert advice about an appropriate school environment.
I wish you and your son all the best.