If the snowcats that you are using have a heated cabin, beware of humidity! People go outside, snap a picture, track snow back inside, and it becomes humidity.... as well you have breath and perspiration... it could be very humid inside.... might be time to invest in a pelican case....
Don's right - this is a major factor. Heated or not, there will be plenty of bodies in the vehicle to fog up the windows. Garbage bags for the camera and lenses, for sure. And put it in the bag BEFORE you get in (or back in) the snowcat.
Assuming your trip is the standard from West Yellowstone to Old Faithful:
1. The cabins of the snow cats are crowded - most of that gear list would have to go on the outside (roof) or back platform with the skis.
2. Unless you're on a special trip, not everyone is a photographer so the time for photography will be limited on the trip in / out. Probably not a lot of time to set up tripods, etc.
3. After you get into Old Faithful, you can certainly spend quite a bit of time around Old Faithful and Biscuit Basin by ski or snowshoe. The various geysers are always interesting. There's also a must-do trail from Old Faithful that takes you up a ridge overlooking OF and the lodges.
4. The snow cats will also be available for group day trips. They'll take the group out to various destinations and you ski back. That way, you can spend more time on the photography.
For gear, I'd say your list is much too long.
1. The 24-70 f2.8 II is mandatory.
2. Pick either the 300 or the 70-200. I think I'd lean towards the 70-200 for the convenience of the zoom. Maybe bring the teleconverters but changing lenses and converters in the wind, snow, and cold is tough.
3. Its nice to have a backup camera but you might consider just the 5Diii
The thing is, winter is a different environment and you'll be carrying a lot of other stuff - so plan on lighter rather than heavier. A good pack is important.
Canon specifies the low working temperature of the 5 D (and I assume the 1Dx) as 0 C. It can certainly get much colder than that in Yellowstone during Feb. I've used my 7D in near 0 F temperatures but YMMV.