The only fish I have found that won't eat anything (i.e. flake to brine) are those who only accept live foods. But, once adapted they will eat almost anything. I had a mandarin who ate flake (until he found his way into a powerhead).
Stay away from brine, besides being not real nutritious, fish love it, its like heroin. You might even try soaking the food in brine for flavor if they are really stuborn.
Try mysis. And like I said bite size they probably didn't try it becasue it was too much work (you could try a garlic press). If you overfeed (fat fish after feeding), they are likley to be more selective. Starving should work, just watch the smallest or weakest fish. Shouldn't require more than a day or two.