A couple of months ago now I added 5 new pullets to my flock of 4 hens. They were a little smaller at the time but have now grown to roughly the same size as the older birds. When I let them out on a morning, all of them go for the feeder but after a few seconds the older ones go for the new girls and they are scared away. Sometimes they go back but sometimes they stay away. When I get home from work I find that the new girls have gone back inside and are on their perches, presumably because they know they are safer there. It is nothing too bad but I had expected the pecking and chasing to have stopped after a few weeks. When I can I stay outside to make sure they stay out and get food and water. I have thought about locking them outside to force them to get along but it would have to be after everyone has laid and I am at work by that time.
How much space do they have? I've always found space to be my friend when integrating new birds - the more of it they have, the less jealously do the older birds guard the space against the new, younger birds. You might try setting up multiple feed/water stations. That way the new girls will be able to eat and drink as the older ones won't be able to keep them away from all food and water at the same time.
