Your mom is likely superstressed as a result of the situation, Flower.
Is she strong enough to be able to say no to your son?
If not, could your uncle stay with her for a bit or be available if your son comes back?
Normally, I would say it’s your mom’s choice, as to what she wants to do with her grandson, but I have an elderly mom who cannot possibly stand up to her alcohol addicted son and put him out on the street.
So my other brother and I go over periodically and read him the riot act when he has been mooching money from her or being snarky.
It puts him in line until the next time.
I hope this works out. Know it’s a heartbreaker for everyone.