My mom has similar issues. And I'm able to somewhat enforce "no human food" when I'm there. However, when I'm at work or out, all is fair game.
Good news is, I've made a deal (for lack of better word) with my mom. She can give M/Z human food BUT! only what's on the list that I have made. It consists of some fruits, veggies, rice, chicken, etc...
I think your biggest obstacle is yourself. Try to change your giving in habits bit by bit since it's next to impossible to change over night.