you would be better to keep them in the same cage especially in the winter, they will help keep each other warm by snuggling together. if you have them in a rabbit coop, you will want to put plastic to block the wind from below (not under the cage but around the legs of the cage. drafts will kill chickens the fastest.
thanks for the info very helpful. Im not sure if we are going to start soon I have to find out what the laws on living in town and if we have space in our yard. Also I dont have any coop but know someone selling a rabbit cage that to me looks like a coop already it has two cages stacked and is about 3 or 4 feet by 2 feet and each cage is about 2 feet tall. I was thinking about just keeping two chickens one in each cage, maybe get a couple chicks and raise them inside first. I was thinking about golden sex link for a breed, from what I read in the breed secion here they seem to be the best for both cold weather and egg laying.