Ok, just heard from the vet. They have a heavy load of capillaria (round worm). Since the adults have it, I guess I have to treat all of them....
Do yourself and your chickens a big favor and put you entire flock on a schedule of preventive maintenance for roundworms. If your birds have a heavy worm load then the soil in your coop, pen, run, and yard are already heavily contaminated with roundworm eggs. It will then be just a very short time before you will have to go through the whole worming thing one more time, all over, yet again..