What does your run/coop look like? And what are the numbers of birds in the older group, and number of birds in the younger group? And the dimensions of the coop, roost and run. Often times space is an issue, and what was plenty of room when they were chicks, rapidly becomes not enough room when they approach full size.
You might try:
- adding clutter to the run, so as to give hideouts and escapes
- getting pin less peepers - small set ups get very good results with these
- make sure you have multiple feed stations
- you might lock out the original group and lock in the new group. Leave the old group out until nearly dark.
- try creating false walls with cardboard and duct tape to section off parts of your roosts
- watch them closely, and pen up the two or three meanest ones, if you move them out of sight for a week or two, the originals will forget them, and when you add them back, they will be busy working on their own spot.
Mrs K