Welcome to BYC. I will tag some folks that know, and have pigeons as I do not, and see what they have to say.
@WVduckchick ,
@Pyxis ,
@backyard pigeons .
Could you post a few pictures of the Bumblefoot? Could you also post a few pictures of their pen area? Bumblefoot can occur when birds are kept on exceptionally hard, and unforgiving substrate material for longer hours then there intended to be. Birds with conditions that are causing them to apply more pressure to one foot then the other area also predispose them to this condition.
I would not use Penicillin, for one major reason. The bacteria that often cause's Bumblefoot, staphylococcus aureus, has built up a strong resistance to "cillins". If you were to choose to use an antibiotic, I would suggest something like Cephalexin, Ciprofloxacin, or Enrofloxacin.