I put up a tempory fence and sectioned off a part of the run. Had the newbies in there for a couple of weeks. I took them in at night, but during the day they spent it in the run with food and water and a dog house for shelter if needed. That way, the older hens and the newbies can get use to each other without bloodshed. Then I let them in together and watched closely. Yes, there may be some pecking, but usually the young ones are faster and can get away from them. When it's time to roost, the newbies are gonna freak out, and they are gonna have to work themselves into the flock. I actually had a separate roost for the newbies for awhile so they can get use to the whole ordeal. A sawhorse works great!