Most 4-year-old boys are wilful, it seems to be a stage they go through, too old to still be toddlers but not old enough to be "big boys". Girls aren't little angels either. You have to be more wily than them, and not be phased by their trying to demonstrate how independent.
I would try to avoid being too authoritarian about things - If there is an either/or choice, then casually enquiring which they will be doing often works, as they are too busy deciding between them to notice that someone actually is telling them what to do.
If they won't eat what you have cooked, then they can go without, but don't make anything else. You could say "I'll have this, then," and proceed to eat the lot. If they say half an hour later that they are hungry, start cooking them the same thing - any objection and the answer is "This is what there is."