I usually just buy a can from the tractor/feed store for like $5. It looks like this:
So I'll do my best to draw it for you. :D click to make it bigger
They may require a better diet. It could be a molt and the scabs are probably from picking at each other. Perhaps you can provide more food and treats. I would also recommend doing an inspection to your coop and run to assure their predator proofing. They hens could be pecking each other due to...