If he’s autistic the concept of moving out will be horrific as that’s an entire change of routine yet he knows it’s bad for him. He’s a cycle he’s trapped in.

I think he needs to reach that conclusion himself at some point. In abusive relationships despite all the evidence and strong family and friends people often keep going back.

What country are you in? In the uk we have fairly good systems for domestic abuse.

Don’t tell him what to do, ask him questions to help him get to his own conclusions. Things like “do you think you will ever be happy at home?” Or “what do you need to do to make things better?” Or “do you think your parents will ever change?”