I fed my guys individual twice a day until their little bellies we're plump and happy. A general rule of thumb is that their bodies should be as wide as their head. Babies need all the nutrition they can get since they are growing so don't worry about over feeding. I always dropped the food in and let them find it themselves so that when they got bigger I didn't have to worry about an axie that was trained in hand feeding. After leaving food in the container with them for about 30-40 minutes I would remove and leftovers. I continued to feed my axolotl twice a day until they were about 4 inches long, then I switched to once a day simply to save on food.
After feeding you should change the water as the food may change the water conditions, or you can always feed them in a separate container. Another thing you should be cautious about is how much oxygen they are receiving. Make sure that there are holes in the lid of your container, and if there aren't try to find a cover that won't seal air tight. I wouldn't use a towel as some people suggest. . I tried that once and the cloth fell into the water and soaked it all up ( luckily I found my little guy in time and he is just fine now )
As for the bullying, its something that the young axolotls will continue to do until they are more mature. They can be cannibalistic as you found out with your little one, and the only way to prevent injury And death is typically to separate them all.
I hope some of that helps you!