Sorry to be out of the conversation for so long. You guys are right. In the wild they eat various ants that provides the toxin that accumulates on their skin. Mine are fed fruitflies(flightless)/bean beetles/springtails and are thus perfectly safe.

It is ok to mix the breeds as long as they are similar size and have plenty of room. However, once they get to be adult size, you may need to separate them if they are attempting to breed. Also, since these guys are endangered in the wild, it is a no no to hybridize (FYI).