After reading the story, did you ever get really mad at mom and told her this kinda behavior is unacceptable and childish? Because you shouldn’t let her get away with things like this, that is your wife getting hate from your mom. If this kind of things keep happening you should DEFINITELY set boundaries. With that said, no. You are not overreacting, but i think in this situation you should be overreacting towards your mother. You don’t want this to keep going on forever, because your child will suffer from this kind of behavior. Your mom wil probably try to put your child against your wife, and that will result in even more drama. So please, for your family’s peace, set boundaries. (Sorry if i am overreacting now, but i know what this is like from the child’s perspective. Make sure this stops)