The girls with the bald areas on their backs were probably bred too much from all the roosters, they end up tearing up their feathers and can even injure them. The chicken with the very bare, behind may have mites - have you checked her and the others for mites, lice, worms. ON BYC -"everything else for sale," some ladies make & sell hen aprons. This fits on them and protects their backs from roosters claws - it also covers the bald areas letting them heal. You are very nice to take the birds in such condition- I know they will be much happier at your house but, hope the man didn't send them full of parasites /or disease.
