I use daphnia to get my larvae started. There are always lots of different sizes in a daphnia colony, so bigger and smaller larvae will always get a meal. The other advantage of using daphnia is that they will survive for extended periods in the tank water until they are eventually eaten, whereas brine shrimp die quite quickly in fresh water and will cause water quality issues if not removed.
Having said that, I haven't heard of healthy larvae refusing baby brine shrimp, are you sure there isn't some other problem that's putting them off their food? Was their tank fully cycled before you put them in there? I would start with the basics and test for ammonia, nitrite and nitrate and just work through all the simple stuff.
This article is very good if you haven't seen it already.
My axie is acting woerd he was a rescue as stated in a different post he got better and now seems to be deteriorating again...again all tank conditions are OK and as should be. He seems to have some black dapple like pattern under his bottom lip? Is that normal? And his two back feet have a little wierd growth? Almost? Tiny tiny tiny lump. His capillaries in his feathers also appear darker and more visible. Any help would be appreciated