I influenced those muffins,lol

They were from me <3
I understand your mum's point of view... I'd have probably been the same way in her place. Have you straight up talked to him yet? I really think he needs someone he looks up to, or admires to give him some advice- and I know you said shrinks don't make a difference, but that's because he sees them as just that. Shrinks.
You should tell him what he's doing to your mum. Since he keeps coming back, he clearly still values his family somewhere inside. Is he so far gone that he doesn't even care how he's impacting the family?