Welcome!
Why do you want to disown him? To keep him from legal inheritance?
You could make a will that specificies you don't want to share money with him, if so.
Your son is 26. You have no responsibility to care for him, pay for him, or even see him.
If he gets violent or threatening, I would suggest, as BabyBlue mentioned, to get a restraining order. You don't need to disown him to set boundaries for yourself.
You can tell your son you love him and you are concerned for him, but even more importantly you are going to take care of yourself.
I am giving you permission to stop putting him in rehab or paying for him.
You can be done.
He will heal if and when he is ready to.
Its time to let him do what he will. Flounder, steal, go to jail - those are all his choices and it is not your job to clean up after him.
You can even set a boundary and say (to yourself and also to him, if you choose) what it would take for you to have contact with him again. 1 yr out of jail? A solid job and sobriety? Whatever you want for you.
We understand your pain.
Stick around.
Peace