We are new to raising chicks. We got 12 babies who are 9-10 weeks old now. Most are fully feathered. We have a couple who look patchy around their chests with the downy. We live in Northern Michigan and want to move them to the coop (we have no older birds to integrate ). Our coop is secure but the temps are going down in the 30’s and the coop holds the outside temps. Our coop size 8x12. When can they handle these colder temps?