Have you been weighing these kittens every day? If so, can you tell me the weights for each? When you say they act like they are getting enough, how are they acting?
Do you feel they are in jeopardy or in any other way that this is an emergent situation? If so, then you would be much, much better off by contacting a local shelter or rescue organization for assistance. Otherwise, the potential for disaster strongly exists here.
If you don't feel the babies are in danger, then it is extremely important that you begin weighing these babies daily to ensure continued proper gain and advancement. If you haven't already, purchase a small, food-type scale which weighs in both grams and ounces. They are in the kitchen gadgets section of your local Wal-Mart and are priced at less than $10. Begin weighing these babies at the same time every day and write it down so you can readily see if there is a decline or failure to gain at a glance. You will be able to catch a problem long before it becomes an emergency.