I agree with Tisha that parenting needs to be left to parents. Step parenting is tough no matter what even when dealing with adult stepkids, we are a blended family as well. It’s double hard if you try to act as a parent.

Disciplining someone else’s children just doesn’t work. Maybe if you had this kid since infancy or maybe if you were in his life for years. Maybe. But at this point I’d let mom discipline him.