Excellent idea.^^^Maybe put the two old ones in a dog crate inside the run, while the pullets have access to the whole coop and the rest of the run, and let them see each other for a week or so. Then let the hens out and watch what happens.
I would do that in whichever coop & run is larger, no matter which group is living in it at present.
(This is in addition to the ideas other people have posted, about clutter so they can get out of sight of each other, and multiple feed/water stations.)
That just makes me a prolific posterYes, and by the way I feel like I am talking to a celebrity. I have read so many of your posts!

That's old school advice.I’m disheartened to hear that I should’ve done this at six weeks because what I read was to make sure I didn’t put them together until they were the same size.