Mother in law!!! 😡

Anyone have any advice about a stubborn mother in law? My child will be 4 next month and is a super picky eater. I know this is common but as I was raised to eat what is in front of me. They give him everything he wants or they want instead of what I want. The whole side of his family say that being the grandmother trumps the mother? I mean wth!! They think I am starving him because I won’t give him what he wants. His pediatrician said if he keeps eating what they give him he will be super obese within a year or so. Help!