For the food, simply serve him what's appropriate and end the discussion. He's 3.
It is perfectly acceptable to tell him he may have more when he's finished his serving, if he's still hungry.
If he has big feelings about that, well, he has big feelings. Reflect them, but carry on with the way things are happening.
Regarding the toys: his "heart" wants everything and his brother to have nothing because he's 3.
It's a stage. Many things are a stage. Mostly you "fix" them by continued teaching, redirecting, and waiting them out. I have absolutely removed the toy from the older's hand and given it back to the younger, and explained that he can have a turn when the younger is done his turn.