How old are the chicks? How long have you had them?
Do you have a temporary place to put them (like a box or container)?
Don't try to introduce them to the rest of the chickens. The hens are too young to adopt them, and any more interaction will just result in more confusion.
I'll cover as many bases as I can think of, since I don't know exactly what your setup is.
First, get a box and a warm lamp. Put a blanket in the box, shine the lamp into it, and put the chicks in the box. That will keep them warm and safe for the time being (just make sure they can't get out of the box!) Next, look around your coop and pick out a corner that you can section off from the rest of the coop. Section the corner off with anything that you know will keep the other chickens out (including a roof). You can probably use baby gates and/or chicken wire. If nothing is readily available, just barracade the corner with whatever you can find. Put the box in the sectioned off area. If you have a heat lamp, set it up above the box; make sure nothing is touching it. If you can't use a heat lamp, get a hot water bottle, hand warmers, or anything else that generates heat over a long period of time. Put it in the box and cover it so that the chicks can't get to it, but they can still feel the heat.
If this won't work, then at least get the chicks to a safe, warm place. Then, post on here what isn't working. It'll be OK!
ETA: Sorry, just looked at your title line more closely. At 71/2 weeks old, they still need to be separated, but they don't need as much heat. They can keep each other warm.
