Chooks won.....

Is there power in your coop?
I would keep them in the garage in a brooder/ grower pen until they are FULLY feathered. They need the heat light for a couple weeks when they are young but will IMO need some heat until they are FULLY feathered.
Also if they have to be locked up in the coop with the grown chickens there may be trouble for them. The grown ones may not take kindly to having youngins moving in on their turf. The babies must be large enough that the older hens will not be able to easily mutilate them.

IMO you will have chickens in the garage or basement or spare room until spring.

I made a brooder box simply enough out of plywood and 2x4's with a wire top. It measured 3x5 and was 30 inches tall. I know this sounds large but I wanted mine to get grown some before putting them outside. Just a thought on how you could corral them in the garage.

 

We bought a wire compost bin set (3 bin set at Gardener's Supply) and zip tied them together -even over the top so no little chickie girls would feel like flying out and pooping all over the garage. Put in a dog crate in case anybody wanted to get cozy and a couple of roosting bars across through the wire. When it got really cold over the winter (cold enough to ice over their water IN the garage) we added a heat lamp hanging from the ceiling. Straw and shavings on the floor cleaned weekly and everyone was happy! We kept the enclosure set up as an "teenager pen" after the big girls went back outside and the teenagers were fully feathered and ready to go out the their own coop.
I can't tell you how many times I would find my husband out in the garage feeding the little girls and talking to them. We got lots of wierd looks from people when we mentioned the chickens in the garage, but they did well.
Good luck!
Deb