I would provide separate tanks for each cray. 10 gallons is just about right for one. If they were all getting the same amount to eat, they would all grow at the same rate. Being 'Krebs, they are genetically the same. In a 10 gallon tank you don't have much margin between feeding just right and over feeding and fouling the tank.

Set up a big tub outside. 'krebs are cold hearty as long as they don't freeze. A non-metalic stock tank works well. I feed mine sinking trout pellets, and that works fine. They also get some duckweed when they want it.