I would probably buy 2UYs. October for BR and and Feb for BW/BC.
@Sandisw is spot on about travelling early in your UYs, I just have reservations about December. That is a tough time for
DVC rooms. I own at BR for the purpose of going 1 of the first two weeks of December. December 2020 was tight with availability at least for studios. If you are talking early December, I'd want the ability to walk a reservation if needed, and a Dec UY may not work for that.
One other thing, if you go first week of December and arrive on a sunday, that could actually be Nov 30th or so. Just a thought to consider, I do not know exactly what you are thinking as for times.
Halloween is 2 months long at Disney, and for the most part, all of it low/lower crowds. So much flexibility for that holiday. Its a trip I tend to make, and never worry about it for that reason. If one week isnt available, Ill do another.
Christmas is Thanksgiving to Christmas, about 4 weeks , and only 2 of them that have tolerable crowds. Its a narrow window, and I would want the walking option open to me. As well as Nov. 29th, 30th,