Were they wild caught or bred ? Because if they are shriveling up, this sounds like Chytrid. It attacks the keratin in the skin and stops osmotic regulation (the controlled flow of water in the skin). They retain some water in their body and die of cardiac arrest. Other tell tale signs can be digit (finger, and toe curling) hyper-sensitive skin (they almost seem in pain when being handled.) Tadpoles are carriers of chytrid due to lack of keratin in the skin. It stays in their mouths and can cause lack of pigmentation and mouth deformities. Once they metamorphosize the fungus is able to take hold of them.

I'm very sorry for your loss, I saw this thread while I was replying to someone else's situation which was similar and decided to take a look. Good news is though that it is possible that the ones that are still alive could show to be immune to chytrid or whatever pathogen is causing it. My recommendation is the same as it was ot the other poster, if you can take them to a vet who deals with amphibians and they can test for things such as ranavirus, chytrid, etc and possibly treat it depending on how far along the illness is and what specifically is the problem.