The reason firebelly toads have the bright orange bellies is so that they can flash them to warn predators that they're toxic. The toxins ooze out slowly and will eventually kill the other frogs in time. The only time the toxins come out promptly is if the toad is eaten. Please remove any frogs from the firebelly's enclosure that are not firebellies, especially if they're wild caught.

As for the toad, I would try to find a vet for him, and get him set up in a separate and small enclosure, to help him catch bugs.