well as far as sexing them...if they are not matured at all yet then you might not be able to tell. When they are getting sexually mature, the male gets little pimple looking things on his front arm pits, and the male is more narrow shaped and much smaller than females, but they are social creatures and live fine together as far as I know. I have never heard of anyone having a problem with 2 males or 2 females if that is what you have.
As far as the Chytridiomycosis, I had 2 frogs die from this recently. Apparently it is making its rounds in the herp community like crazy. What are your frogs symptoms? There are a really WIDE variety of symptoms including reddening skin among other things. My frogs actually looked like they were seizing at the top of the tank and then they just died....however there are a LOT of symptoms that can present. Would definitely help if you could list the symptoms and maybe even get a picture.