I’m not a professional but I would look for a neurologist that specializes in autism. Please note My tone here is one of compassion, and I’m just tossing out ideas that could possibly help. Forgive me if what I’m saying is obvious and you’ve already tried these things
Small possibility his behavior could be aggravated by a food allergy ( not caused by)
I would contact your local chapter of Autism Awareness or Autism Speaks. There are people that can come in your home and help you
Honestly don’t feel ashamed. There are professionals with years and years of schooling that need support from colleagues to determine the right action plan for an adolescent. Every child is so different. it often takes a village and not just one neurologist.
In the meantime while you are waiting for a callback or getting ready for an appointment. Think about maybe a small diffuser of a scent he finds calming. See if you can get him to use up some of his energy
Run with your kids in the back yard or chase them.
Give him a task , does he like taking things apart or putting things together?
Put reminder signs with rules and enforce them. As much as you can. Get rid of sugary snacks or lock them up and use a small one to reinforce good behavior. Some children really want boundaries, it helps them feel safe.
As a parent you are exhausted, but following through is important. Reminders of Family rules would be helpful . Everyone needs to be in the same page. I have helped a family in crisis before, but as soon as I left my suggestions were ignored. Nothing changed and the house became even more chaotic and the behavior became more oppositional. As a family unit, maybe have your other children take pride in helping and engaging their brother.
Please let me know how it goes.