I introduced the new hens as 2-3 week old chicks in a separate penned area in the run for several weeks. The original flock could see them, but didn’t really take any care/notice of them that I saw.
The coop is 12x12 with lots of roosting bars and nesting boxes. The new hens can get to the roosting bars, and do go there during the day to avoid getting picked on.
The run is 12x15 with a ramp leading into the coop and a door that we open and close to allow day free range in the pasture. The new hens go out to free range sometimes, until an older hen chases them back into the run. When the old flock comes into the coop at night the new ones head to the run, there are places to roost, but the new hens all hang together and won’t sleep in the coop at night.