I have a coop I built for injured birds, to keep them with the flock, but safe from dinosaurish behavior.
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I have no injured chickens at present, so I put a bunch of hatchlings in it and am using it as a tractor coop. See how I've propped the front door? This allows the chicks to go in and out, but it's too narrow for biggers to get in. (I usually have the lid down, but I wanted to photograph the inside.) This way the smaller birds have a safe location to retreat to, should the biggers get too violent.
At present the chicks have integrated well and the only reason I have the front door propped open just a crack is to keep the olders from stealing the chick developer food. So it's basically serving as a creep feeder and a bedroom/shady retreat for the chicks. You could do something like this, modified to meet your needs.
I integrated my four silkie hatchlings and their Brahma hatchmates using this "hospital" tractor in the same way. They've since graduated to the bigger tractor (in the background of the second pic) where they sleep with the hens and ducklings.
These and the little green broody coop (1st pic) are enclosed with solar electric poultry netting which I open in daytime so they can all free-range together. This allowed me to integrate two batches of chicks with no violence and no disruption. I'm really glad I took the time to build it. You would need to modify anything you might build to suit your needs, but this is an easy, inexpensive tool--very useful to me.