I agree that all of the photos show bumble-foot looking lesions. Normal chicken feet to NOT have black scabs on the bottom- as you said all of your birds have this. You need to carefully check your coop area for what is causing this, as there is a serious problem with it. 2x4s make great perches if you sand the edges. A 'plank' is not necessarily a bad perch, if it does not have sharp splintered areas. What is under the perch(es) where they jump down? What is in their chicken yard? Check for exposed nails on things, sharp rocks, jagged metal- things that would cut a chicken (or ducks) foot- to get bumblefoot, all that needs to happen is a cut or puncture to the foot and soiled skin or dirty ground. You need to treat all effected birds, and find the cause- or this will be a continued problem.
