Help!

Need some insight on what could be the problem here. I currently have 6 hens. Plenty of space to roam in the coop and I let them free range a few hours at least every day. I clean the coop regularly and they dust bathe frequently. They pick at each others feathers and backs, especially the ones in the pictures, and I can’t figure out how to get them to stop. I feed them higher protein feed and clean fresh water. They’ve been this way for months and I hate the way they look. Any ideas???? My black hens and the one RIR don’t have this issue although just recently I’ve seen some bare patches on the necks of the black hens. The ones with almost no tail feathers seem to be picked on the most.