Never seen one eat a frog, I fed quarantined guppies/rosy reds when they are smaller. Try and wean off live food if possible and gradually switch over to nonlive such as frozen silversides, tilapia filets, etc.
Depends on your tank size but it sounds like your pretty well stocked as is. They are rather skittish and need alot of open water to swim, if the tank they are in is crowded they really wont do as well.