Alright, looks like one of them eats lance fish. Took him a few days of nitpicking which piece he wanted and which he didn't to finally gulping any lance fish that hits the water. I tried tricking him into eating a pellet, he tried, and spit it out, oh well.
As for the other one, I had to overfeed the first to allow it to try, he follows the food in the current, then decides he doesn't want it. Improvement, but this one's not quite eating dead yet.
They don't even want to see mussels, though.