Typically feather picking is caused by boredom and overcrowding. It can also be a lack of protein in their diets. You can throw some dry cat food out just as a treat to up their protein. Don't overdo, though. And look for ideas on things for them to do; you might try a suet feeder hung from the ceiling, stuffed with a healthy treat such as greens. It takes them time to peck it out of the suet feeders, so they are distracted with that and will thus feather pick less. Good luck! Sounds like you're getting good advice, and your birds appear to be healthy otherwise.
ETA: If you have Buckeye feed available to you, get some Layer/Breeder; it's got higher protein (20%) and animal protein. I switched to that (it comes in a pellet form as well as crumble) about 6 months ago and have been VERY pleased.