Camill,
You have many options..
First you need to find the cause. Chickens eat feathers for a reason..they are lacking something or they are sicks, or bored. So you need to find out why. I think I know your set up. You have enough room unless you got a ton more birds that I do not know of.
are you still feeding FF?
ACV in the water?
I would take a sample of poo to the vet and check for worm load and cocci
This is our coop.
I stopped offering the fermented feed after it got mouldy a third time. I havent given them acv in a while I need to start adding it back into the water. I will try offering meat. I was also suggested for the badly plucked two to use blue kote. Im hoping its not that there isnt enough room. They are always scratching and active and seem to enjoy themselves.