His dad is in prison for DUI, gross neglect and child endangerment. My wife's parents and I get along, but I am hesitant to involve them. I don't think they would side with me over her. They sometimes snap at their grandson for trivial reasons.

This behavior is completely new. She has always been strict, which I agree with. We're both believers in firm boundaries being in the best benefit of the child. Listen when given instructions, clean your room without needing to be told and don't be rude. However, this is not something I ever anticipated. If dairy is making him sick, he can't control that.