My wife did survive her son's attack. He didn't do much damage. If he had really wanted to kill her, he would have.
Much has changed since then. Difficult Stepson is better in some ways, not so in others. His younger brother is our current concern.
I would think your son needs not a boarding school, but a locked, therapeutic residential placement where his aggression and violence can be contained, and he can receive the help he so desperately needs. Maybe that is what you meant?
It is devastating when we are brought face to face with the reality that our children are not able to function the way most others can.
Your son, unfortunately, won't grow out of reactive attachment disorder. As you say, he has displayed problematic behaviors from infancy. He needs an environment where he cannot harm himself or others. Unfortunately, no home environment, no matter how well monitored, can provide that.
I am sorry.
From what you write it sounds like you have many resources at your disposal. He already has an IEP and a special program at his district as well as private counseling. That is a good start.
His psychiatrist might be able to help you get started on the path to an out of home placement.