Brine shrimp eggs hatch in about two days. From that point on, baby brine shrimp (bbs) lose nutritional value and begin to die. One hatched batch is only good for about 2-3 days, so the ones you started last week are either not hatching, or are too old to use. As the larvae don't eat for the first couple of days, it works well to start the bbs hatch the same day the axies hatch.
Like fish, you feed larvae as much as they will eat at one sitting. You have to very carefully remove all uneaten bbs, as they die in fresh water and contaminate the tank/container. Feed them at least once per day, twice is better.
I've raised axies in small groups, like 4-10 per container. If they are well fed, separated by size/age, and kept at a low density, cannibalism is rare.