As long as they have a draft free place - and in that case, well ventilated but not tons of space per chicken - they help keep each other warm.
So, good HIGH ventilation, without drafts and they should be okay. If it is really windy, too, try to add some supplemental heat. I don't have electricity at my coop, so if it is really nasty, I take a 5 gallon and fill it with hot, hot water. Wrap it in corrugated cardboard...and put it in the coop as a mild heat source. It helps some!
As a last resort, some people find a place in their house or garage to move the chickens to if their coop isn't set up for that level of cold, or if they are molting or sick or whatever. Cellars would work well if you have one - cooler than the rest of the house, but not frigid, and easy enough to put shavings down or an old sheet to make for easy clean-up, and a step ladder or a 2x4 on cinder blocks or something serves fine as a temporary roost....a cardboard box with shavings or an old towel serves as an acceptable next box.
Chickens are pretty hardy and cold tolerant as long as they have a draft free shelter......best of luck figuring it out for yur circumstances!