I disagree that this is Bumblefoot, at least I've never seen a case like this, nor have I seen Bumblefoot on the webbing part of the feet. What are the birds being housed in, and how often is it being cleaned, birds can suffer from ammonia burns on their webbing if they are sitting on fresh feces for an extended period of time. I agree, with disinfecting it, but the underlying cause should also be addressed or it will most likely reoccur. Cephalexin can also be bought as a Fish product online or at places like Petsmart, TSC, or Petco, Its often used for treating skin infections.