How long have you had the barbs - because from what I read, they are usually the ones that eat all the food before the other fish get a look in. If they are new, they might not have settled in yet, then when they do....
The way to make sure all the fish get enough food is to feed different types of food. Surface feeders get to floating flakes first. Mid feeders will get flake if you soak some of it before feeding as soggy flake sinks faster, and slow sinking pellets. Bottom feeders need fast sinking food, usually pellets of the type to suit their dietary requirements (algae based for vegetarians, meat based for carnivorous fish). Again, pre-soaking them makes pellets sink faster. Nocturnal fish, should you ever get any, are best fed just before you turn the room lights off for the night so the daylight feeders go to sleep before they get chance to eat the food.
Another trick is to feed the greedy fish at the opposite end of the tank from where the slower feeders are, then when they are stuffing themselves, drop some food in for the slow eaters. Using a turkey baster to drop some pre-soaked food right in front of the slow feeders also helps them get it before the greedy fish notice.
Edited to add the word 'room' to feeding nocturnal fish - feed them just before turning the room lights off for the night.