You're on the right track by dividing the coop.
Is it divided with some kind of mesh so they can see each other?
That will help everyone get used to seeing each other in the same space.
Most folks don't integrate until the pullets are about the same size as the hens, I'd keep them separated for another month or more.
There's lots of variables to take into consideration as you figure out how to integrate.
-The more room the better.
-Multiple feed/water stations.
-Places the youngers can hide/get away from the olders.
There will always be a pecking order and it takes time for them to figure it all out. As long as none of the pullets are being trapped or bleeding, let them work it out. If you separate then reintroduce they'll have to start over sorting the pecking order.
The longer I've observed them doing what they do, the more confident I become in recognizing the difference between acceptable and not acceptable behaviors......they can appear to be mean as heck, but it's just how they roll. A bird can deliver a seemingly viscous peck and the pecked will run off squawking like death is chasing them..... for about 3 seconds, then go right back to toodeling around like nothing happened.
I learned
a lot and got some great ideas by reading to see how others have accomplished integration:
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Good Luck and Have Fun!!