Hi and welcome!
I agree with the guppies; fish have always seemed to be a big hit with mine. Also, do you leave them together to eat? Sometimes if they're all in the same area and one starts eating it will encourage the others (of course, some snakes just freak out if anything is going on while they're eating, so I guess that's just sort of a 50/50...)

Also, salamander tails? Are they wild caught or from a supplier or something? Haha, I've never heard of that, but sounds interesting.

Good luck with the babies!