I would divide your babies now into the groups you want them to be in and brood them where they will live permanently (next to your older birds). If you have 2 heat plates it should be easy. I agree it's almost like integrating the 4 in with the babies. My chicks are almost 3 weeks old and my older hens have been somewhat afraid of the new babies, I'd hate to see what happened if they never met until later, especially with a larger group like you have.
I used
@aart 's method of integration last year and again currently, very easy and peaceful.
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If you can just make some sort of divider in the coop between the chicks, you'll only need it for a few weeks. I start with HWC divider (middle pic) for a week or 2, then switch to something the chicks can come and go through but hens can't fit (3rd pic with 3.5" spaces) for another week or so. The babies will gain confidence and follow what the older birds do and start roosting on their own.
If you plan for both flocks to range together at times, it would probably be a good idea to also get those groups together as often as possible in an open area so everyone is familiar with each other. And have multiple food and water stations available to help reduce squabbling.