Switch the door knob so the lock is on the outside and lock him in. Sounds harsh but I’m a twin mom too and while we aren’t where you are yet, when we get there I won’t hesitate to lock my children in their rooms for safety. Alternatively you could Change the door handle out from a round knob to a long handle and try this on the outside: Door Lever Lock (2 Pack) Child...
I live with my 4 year old who has autism and a 70 year old man with Parkinson's disease and they have worked WONDERFULLY.