Hi R,
I'd never heard of bumblefoot. Had to look it up. I actually look it up in a book called the smallholder encyclopedia, circa 1937. The then remedies were as follow: If abscess is soft, lance it and disinfect appropriately; if hard, paint some iodine and bandage up. In either case, keep separated and free of dirt.
If it was me, and be sure to understand that it is not something that I have done in the past, but if it was me, I would separate the
chickens and put them in a clean and dry environment. I would then make a mixture of turmeric and and echinacea tincture with a few drops of tea tree essential oil, put it in a spray bottle and spray at least half a dozen times a day. I'd probably put some echinacea tincture in their drinking
water also. I'm sure there are other remedies but this is what I have on hand, and this is what I would use to start with. You can make a paste with turmeric and water or even echinacea tea if you don't have tincture.
Maybe someone with better knowledge might be able to help. Good luck with your birds.