I keep a variety of foods on hand. Also with Biota they try and list what food they fed so I try and have that on hand. Knowing they are on the smaller side I'll go with smaller dry pellet. Frozen I use LRS Reef Frenzy, LRS Reef Frenzy Nano, PE Mysis small, and v20 arctic e-z pods. I'll buy in bulk from premium aquatics as they do an amazing job of shipping frozen with a good price. Dry I keep TDO chroma boost x-small, small, and medium. Hikari marine s, marine a, and pe mysis 1 mm pellet.
I'll feed 1 at a time, small amount, to see what the fish eat. Make a note, then next feeding session try a different one. Within a couple days I have a good idea of what they strike, consume, and if they have a favorite. My pink squares 3 out of the 4 ate everything. One that was on the smaller side only wanted the TDO x-small pellets. Now it eats all pellet but doesn't like frozen - go figure :D
The fish you are talking about - regal and multibar - are pretty. All the best to you!