Yes, you can have them molt in the dead of winter. And yes, some are going to look terrible, like they partied all night and stumbled home with only part of their clothes on. And even if it is 20 below, they do fine.
Some molt hard and fast. You can open the coop and think something was killed, there are feathers everywhere. That bird will have more feathers off of her, than feathers on her. Personally I like this best. I know it is molt, that is what is happening, and they tend to grow new feathers fast! Then they look like they all got new Easter dresses.
Other molt slow, these can be alarming, cause you are kind of guessing; ''is this molt or is something else wrong?' They get patches, the neck, heals up, the breast, heals up the tail, heals up and then one day you realize they are all feathered and pretty again.
But even though it seems terrible, it is a natural situation, and truly does not bother them too much, sometimes they are grouchy, but they are not dying even in pretty cold weather.
Mrs K