You cannot keep 8 birds in that coop. It is a very common piece of misinformation that is often included with those pre-fab coops unfortunately.
If you could make the half of the pre-fab run that is furthest from the ramp predator and rain proof, you could put the two new girls in there with a perch for roosting, food and water and a covered nest box. Basically a small coop within that run. It's the security issue that might be a challenge. I don't know what kind of predators you deal with there.
If you decide to do this, you will need to have Corid on hand and watch for signs of coccidiosis in both sub-flocks as they can expose each other to the strains they carry but have developed immunity to.