ok, I'll give this a try.
First off, move the still alive frog into a smaller tank with paper towel substrate, a water dish and something to hide in. Keep the temp warm and don't check up on the frog every ten minutes, this will stress him out even more.
Secondly, get rid of the moss, this can cause impaction and the crickets can hide in it. Use coco bedding, like bed a beast. Safer by far and you can plant in it well enough.
As for UV, not necessarily usefull at all. White's sleep all day so don't get much exposure to it. Use supplements to provide him with the stuff that nature gives him.
A heat lamp is not necessary unless the temps are really cold in your house. Don't turn it on unless you have to, as it dries the air and the frogs. (note: I do use one when I need to, but don't use it to controle the temp in the tank.)
The blister could be alot of things; rubbed against something that aggravated his foot, a cricket got hungry and munched on him or it could have been there previously. (poor living conditions and such before you bought them)
Just a note, to avoid possible heartache next time, make sure you do research and find out what a healthy animal looks like. Don't buy them if they are not healthy looking. You can even ask a pet store person to dangle some food in front of them or something and see if they eat (if they don't eat, not really a good idea to buy). Rescuing animals is a knightly thing to do, but you'll just have trouble with it afterwards and the animals may or may not make it. If you bought these two from a breeder, then maybe next time make sure you have some references from other satisfied people. Especially if you don't know them.
I'm not saying this to get you angry, just a little advice.
Keep youre frog warm, don't worry about food for another couple of days, I know they are skinny looking and you want them to eat, but if the frog is stressed by anything, you should give him a couple days to settle before trying to feed him again. (don't forget to put him in a quarantine tank).
-----
I think my frog owns a megaphone....
White's tree frogs : 1:1
Mantella viridis : 1:2