Thanks for the help everyone!
I have tried mixing their BBS with dry foods, but they only go after stuff that moves! Although if I pour the fine little bits of Mysis into their tank after feeding the large chunks to the rest of the tank they will eat that. Maybe I'm doomed to feed them frozen then.
Of the adults, the female will pick at flake foods, and both will take the odd pellet, but both would probably starve to death if I didn't feed them frozen food regularly. Stupid fish...