Suggest Treatment For Lack Of Physical Growth

My step son has been through a lot in the past year. He has always been really tiny. Last year when he was 4, he was about 28 pounds and a little less than 4 feet tall. He is now 4 years and 10 months old and still only 31 pounds and 39 inches tall. He is in the 3rd percentile for weight and 8th for height. I am worried because I know at mom’s house he doesn’t eat very well. He is extremely picky eater and has a tiny tummy because he only eats like 5-6 bites and is full. At daddy’s we constantly have snacks on hand... He eats only carbs though... Bread with peanut butter, mac n cheese, we don’t feed him chicken nuggets from mcDonalds but we try the frozen kind... nope doesn’t work. He is supposed to have daily vitamins so at our house we give him the gummies from the store. I’m worried that he is just not getting proper nutrition. There is no consistency. At our house we try to switch it up and decrease sugar but he is so used to eating nothing but bread, mac n cheese, and chicen nuggets and cereal at moms. He will close his mouth, put his hand over his nose... gag... when presented with other foods. He will choose to starve than to eat what we want to feed him. When we had him more consistently over summer we got him eating dehydrated grapes, clementines... now we are back to square one with weekend visits. I am not sure what to do. Is this normal? Is he healthy? He is SO tiny and SO picky. I know there is sensory stuff going on, but mom won’t hear it. We have tried everything to communicate with her, including bringing it up in court. What to do to keep this kid healthy. Let me know.