Bad case of scaly leg mites. My most effective method to treat leg mites is to dip their legs in used motor oil. Works every time and I've never had any negative side effects. Try not to get their feathers oily it makes them look dirty. You might have to redip their legs in three weeks to make sure you get them all with as bad as it is now.
I use teramicin spray works a treat quite expensive but I spray once leave 3-4 days and then spray again quick results every time. It's a turquoise colour used to use it on the sheep for foot rot, cuts etc