Merging groups when they hate each other

I'm having trouble merging my younger birds with the birds that are about 4 weeks older. I thought about removing my rooster. He's the worst, but my pullets are just as bad. The older group is about 8 weeks. The younger group has a misfit 8 week old they won't let join them anymore, four or five week old EEs (5 of them), 1 3 week old mutt, and a couple tiny babies who aren't ready to play outside. The rooster makes this reeeeeeeet sound when he sees them and him and the older pullets will peck violently at the other group. Now I can let them all loose in the yard and they are ok. They just form two flocks and keep a distance. But I'm at a point now I need the large pullet and the Easter Eggers out of the baby tub as it's too cramped. I need them in the dog kennel with the others at night, but they'd be attacked! How do I work with them to sort out this dominance problem?