The amount to feed does vary based upon the activity level, calories within the food and the individual metabolism.
Feeding multiple cats is hard when one wants to over eat. A good diet to feed kittens is Royal Canin Kitten Spay/Neuter.
https://www.royalcanin.com/us/cats/products/retail-products/kitten-spayed-neutered-dry-cat-foodIt is formulated for growth but will help to decrease the amount of fat stored in the body. Most kittens will eat about 1/2-3/4 cup at this age BUT this is highly variable.
A good option is to separate the kittens during feeding time into separate rooms with the door shut. Don't leave food down at all times. Feed them 3 times a day. Another option is to purchase a smart feeder that reads the microchips. You can program this to limit how much food the heavier kitten eats.
I hope this helps and please feel free to post any additional questions.