It could take several weeks for them to completely feather out. I would stop the additional lighting, up the protein, and make certain there is plenty to keep them entertained in the coop/run (where ever they are confined). If the vent area does not show signs of growing back feathers, you can slather that area with pine tar - nasty stuff to work with, but I have had success with it. It will protect the area and tastes very nasty, so pecking/picking should stop as long as you keep it on. Avia Charge 2000 is also good to add to their water. If free ranging is an option, that is what I recommend. I have had the best results with that.