Stealing veggies is common. The best food is in the mouth of their cagemate(s).
Try scatter feeding the veggies. My boys do not like to eat out of bowls they tipped them over when I first got them so now what I do is literally put veggies all around the cage.
This way that no matter how slow or fast one Piggy eats they can go to the different sides of the cage. You can also try hiding some food in the hay to give them an opportunity to forage.
Pellets you should only be giving 1 tablespoon per pig per day and what I do is I will put one pile of pellets on one side of the cage and one pile on the other.
Normally though both boys will eat from the same pile of pellets so I can’t win there but my guys generally don’t steal pallets from each other it’s mainly only veggies and hay.
1 cup of veggies per pig per day.
1 tablespoon of pellet per pig per day.