I know how posted this 2 weeks ago and didn't get any responses - sorry for that. It may be because you threw everyone with "red bellies". I assume you're referring to Fire-Bellied Toads. Some frogs (particularly females) are more aggressive eaters than the males, so that likely explains what you're seeing. I would feed them together, just make sure there are enough crickets available that everyone gets a couple.

The back color is not something you can really do anything about. What you've described doesn't sound abnormal to me. On the supplement front, I think you've got a good routine going but I would probably increase the frequency of supplementation to about once every 1-2 weeks.