Well at this point I would contact Dr.Frye, show him some pictures of the Red Eye that died and if you have any of the Whites with the green patches. He'll probably suggest you do a round of baytril on the remaining two.

The problem of getting frogs from places like Petco or Petsmart is that they usually get their frogs from large suppliers instead of local breeders. That means your frog if it wasn't wild caught (by some miracle) then it could have come into contact with other frogs that were wild caught. Then it is put in an enclosure that may or may not have been cleaned prior to it arriving at the store. So who knows what he is carrying. Then he is put into a tank at home with two other frogs from different continents. Each carrying their own toxins and parasites that only they are use to. Sort of like Columbus coming to the new world and infecting the indians with diseases their bodies had no immunity for. Anyway I would treat them as wild caught frogs.

As far as the tank goes....I would gut it and start over. I don't know if you saw my thread: "what does your tank look like?" I posted some pictures...that's kindof what we need to be shooting for when it comes to our frogs. So here is what I recommend :
You are going to need a few supplies:
1. Leca or hydroton (red or brown clay balls) for drainage layer under the soil.
2. Screen mesh the size of the tank to keep soil out of the Leca.
3. Soil...if you don't already have some...discard the old stuff.
4. One huge Pothos or several smaller large leafed indoor plants. See Johns dart frog terrarium build to get an idea how to set it up.
5. Rinse off the plants really well
6. Cover up three sides of the tank and make sure it is in a quiet and dark room. Completely dark at night.
7. Remember a lot of plants...fill it in...they walk from beach to branch.
8. Have your water dish in a small clearing.
9. Try a cricket bowl that will help you monitor if they are eating.
10. 85 degrees is too warm for them...stay around 76- 78.