Re: Brood Rearing Below Zero Help!
From your description seems the cluster is very small. Something that is often not realised is that many bees (depending on strain), do a sort of trade off. If it's winter and they have plenty of bees, they go broodless, which makes sense to conserve food. But if they have a very small cluster they can be aware they do not have enough bees to make it and will go all out to raise brood given any opportunity at all, even when the beekeeper does not expect that. Your bees probably fall into that catagory.
While you do not specifically say, it sounds like you are aware of and have dealt with the mites? If so and the little cluster is healthy, just let them do their thing, they are trying to get the population up to where they think it should be. If they defecate in the hive well not much you can do but it will soon be spring and allow them to cleanse things.
Be sure to keep mites controlled, and other than that just watch them for swarming when that time comes.
"Every viewpoint, is a view from a point." - Solomon Parker