Don't feel bad, I'm sure you've done all you could. Definitely get a 5% uvb, I'd recommend calcium plus LoD and keep temps right 72-80f and make sure humidity is around 60-70%. Imo there's not much you can do to treat frogs, most will die even with treatment because they're so delicate and may too far gone once you see signs of being ill. The key is prevention. Clean the tank and disinfect it with reptile safe disinfectent. Wouldn't recommend purchasing any WC tree frogs (assuming they were) go for captive bred, it ensures you healthy frogs and doesn't support the collecting. The only reason I got WC as I planned on breeding but half mine died and since then I didn't want to take the chance on buying more. Some good books to read are AVS popular tree frogs and tree frog by Devin Edmonds.