So only the rooster free ranges? The 2 hens stay in the 6x12 area? The adult coop is inside the kennel correct?
You're a wee bit snug on space for integration, but might still be able to make it work as it is. You will need to get creative with clutter in the "run" (I'll refer to it as a run since it's functioning as such - might want to consider rearranging everything in there to disorient the existing birds a bit, so they're distracted and it makes it easier to ignore the new additions.
Or if you're okay with letting the older birds out for a few hours, let all of them out and put the new birds in the run during that time, so they can explore it and get used to the space without harassment from the older birds. Do that daily if possible for maybe a week or two, and then try having them all in the run together while you supervise.