It is almost a necessity to feed newly free swimming angels on live food. Their natural instinct is to go for it. I was usually able to ween mine off of live bbs fed 3-4 times a day starting about 10 days after I began feeding. You start by mixing 10-15% non live food with the live. Because of the eating frenzy that ensues, the fish grab for the non- live too. Each day you increase the % of non-live and reduce the % of live. My preference was frozen cyclop-eeze for the non-live but that is pretty pricey. Other high protein fry foods should work fine. It takes about 5 days to move them from all live to all prepared food.
You said you fed the brine shrimp. If you mean adult brine shrimp, they are way too large for angel fry, they need freshly hatched baby brine shrimp. You should be hatching these daily as after 24 hours most of the nutritional value for fry is gone. I used to run two jugs for hatching alternating between them to insure fresh hatches all the time.
It is also important to vacuum the tank after every feeding and especially before the fish sleep. While they may be swimming around by day, at night they go to the bottom. If you fail to vacuum regularly, the crud on the bottom can and will be fatal. They are not good in a 5.5 for more than a few days and you will need to move them to larger quarters. The nice thing about vacuuming up the uneaten food after each feeding as then you will be effectively starting a water change. And they do need clean water with no ammonia or nitrite and as little nitrate as possible.
Most angel breeders will tell you that for each pair of spawning angels one has one should have two 55 gal. grow out tanks. If you want to raise the maximum number of fry, that is what it takes considering they can spawn very 10-14 days.
I used to hatch out angels in a 2.5 gal tank and as soon as they went free swimming began the upgrade process.