Have you tried sleeping with him?
When my son couldn't sleep, I found that sleeping in his bed, with him knowing he also had to stay in bed, was my ticket to actually getting some sleep.
No, it did not become a permanent bad habit. He grew out of it.
But, still, it doesn't always work. The needs of everyone in the family have to be factored in.
_________________
Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).