Another trick, I recently heard, was to put their feed dishes next to the wire that separates them. Eating is a prime time for a peck, but if they are eating together, that is a social acceptance.
However, hideouts are important, and space. Have you measured your set up, and then counted your birds? Often times what seems like a lot of space with little chicks becomes much less space with older birds.
You might tip the numbers the other way. Right now, you have more older birds in their established home front. They are going to defend it and to that you are adding younger and less number birds into a strange place. You might try, trading places with the birds, putting two of the old gals in the chick spot, and one old gal and two chicks together, try and pick the middle old gall chicken. The top and low pecking order chickens are generally the meanest. This will allow the chicks to establish some comfort in the big coop, and while you will eventually add the old girls back, at that time you are adding mature birds, which give them some advantage.
If you have just one old mean biddy, you can pull just her, and get the chicks established with the other ones, and then after a couple of weeks add back the mean one. That often brings her down a peg.