A year ago, my flock began eating any feather that would float free. They weren't picking at each other yet, but I didn't want to see it progress to that.
I'd read that feather eating indicated a possible protein deficiency, so I began feeding a quarter cup of dried cat food (for fifteen chickens) when I tossed out their daily ration of scratch grain. I haven't seen any feather eating since.
However, recently I noticed my youngest pullet picking feathers out of the throat and face and hind quarters of her former brooder mate. Since she's very small for her age, I'm assuming she may have a nutritional deficiency due to being at the bottom of the pecking order, and is feather picking to make up for it. I started her on an ounce of tuna every other day, and it's been over a week since I've noticed her feather-picking.
You might consider that your flock could use extra protein. Feeding some flock raiser with the layer feed could also help since it's higher in protein. Make sure they still get their oyster shell, though.