I had the same integration issues too, 3 pullets and 1 roo that grew up together for the first bunch, and 6 pullets purchased a month later. The 4 were NOT having it, and I had to wait until the 6 were of the same size as the 4. Hubby built a tractor (predator proof) and the 4 lost the coop and run, got relocated to the tractor and the 6 got the run & coop. Tractor was set right next to run, complete with nest box and barn tin for night time. This took 9 weeks, everyone free ranged in the evening for an hour with no issues, but integration was impossible and oh did we have blood. Never thought it would work, but it finally did one night after dark when we made them stay out until all they could see was our flashlights and a solar light in the coop! LOL Finally we have peace! Do you still have your smaller coop? Can you separate them until Spring when the pullets are older?