Hi, Jules. I am way out of my depth, here, but you seem to have identified the basic trigger to the problem: Whatever is going on with him, suddenly living in a family with four siblings is creating no end of stress for him. Bipolar and other mental illnesses have a major stress component. He gets stressed - he flips. This is no fault of your own. It's just what happens when you put a kid with certain vulnerabilities in an environment he can't handle.   He may be in a different environment right now, but his brain obviously hasn't settled down. There are no clear answers, but hopefully with an awareness of the situation things can improve. His incident at school - frightening as it is - has at least put him on the radar. Hopefully, this will lead to more professional attention.   In the meantime, your own kids need you and you need to remain in good shape to care for them. Please take care of yourself and take time out for yourself. Sorry I couldn't be more help -