Is one cat eating the other cat's food? Perhaps they aren't getting their fair share of the food, so they're always hungry?

What I do, and this seems to work pretty well. I have 4 cats. I leave 2 bowls of dry food out for them all day long. They eat this when they're really hungry. Then when I wake up I give them each a 1/4 can of wet cat food. Then again at night when I get home from work. They aren't getting any more food than they're supposed to, but they think they are. LOL

I do have a problem with pigs though. When it's time for the wet food, Our princess will pig out on hers then bully the other 3 out of their food. I have to stand by and make sure they all get their fill.

Yes- giving in to demands will definitely reinforce bad habits. They're just like kids.