The symptoms you´re describing are pretty vague and don´t necessarily mean that your frogs have Chytrid. Many factors (including bad breeding/ keeping conditions, bacterial/ viral infections, parasites, other fungal diseases etc.) can cause this. You can have them tested for Bd (e.g. SDZ Global Wildlife Conservancy - News - Amphibian Disease Laboratory ; but look for other labs)- Chytrid is treatable, but first you have to find out the real cause of the disease. I don´t think it´s the right way to just give up and let them die without trying to help them first.