Hello,
I went on this trip two years ago and you are in for an amazing time. Highlight for me was Christmas Day lunch on top of a mountain on a sundeck, under clear blue skies, warm sun, surrounded by deep snow and watching the skiers. All the chalets in the valley were covered in snow - picture-postcard stuff.
As Austria celebrates Christmas Eve rather than the day itself, the large Christmas market was open in the afternoon, then back to the hotel for a slap-up meal. Memorable!
Weather permitting you are in for a really good holiday.
Enjoy!