I’d give the kid a simple ultimatum;get out now or get written out of the will.
I’m nys it is easier to leave an adult child out of your will than to get them to leave your home. As long as its their legal address you cant even change the locks on them. You have to go to court for eviction. In a will just leave them 10 bucks that’s it.
That’s when you secretly find “a guy” — a scary one — to have a heart-to-heart with the tresspassers.