In Eastern Ontario, Canada, my winter temperature, Jan. to March are -20C/-4F. There is also an average 250cm/98inches of snow. The ducks, peacocks, chickens and guinea fowl all do fine. Each group has a coop with an attached run. They have a choice during the day where to spend their time and if the sun is shining they are out.
My ducks haven't had their swim pool for several months. I take out fresh water for them each morning in a container big enough to submerse their heads. No water in the coop at night.
IMO the important thing is that they are protected from winds and freezing rain. I tarp the side of runs where the prevailing winds are. Ducks are equipped to survive the cold with feather coverage (think down blankets and coats) and adapted circulation system.
From the description given by DuckMom2022, I would actually be more concerned that there might not be enough air circulation. I think excess humidity is a greater risk than the cold.