I didn't read the whole thread...so excuse me if I'm repeating info.
Give them sunflower seeds....it has melanine, or melthione, or something like that in it that chickens can't find in nature easily. It's cruitial for good feather growth....and if they can't find it, the first thing they do is to start eating feathers.
Try it....it's cured all my feather eating rescues in a day.
Good luck