Tein,
You need to keep your reasoning centred around your children.
Christmas this year falls on a Tuesday - what would be the contact arrangements for the weekend before Christmas? If it is your weekend, then how about suggesting that she has the children that weekend, and you will collect them on the Monday (Xmas Eve) and return them in the evening on Xmas day?
However, if she is working most of Christmas, and Xmas Day is her only day off, then it wouldn''t be unreasonable for her to have them that day.
Birthdays, Christmas, etc are always a bone of contention. Children quickly get used to the idea of two birthdays, two Christmases, etc – and often enjoy this more than we as adults would think. Don''t get all worked up over the date on the calendar – you can still do all the usual traditional things, just be a few days earlier/later if the children are spending the Christmas period with their other parent. Its about the day you all have together, not the date you have it on.
I don''t always think that sharing Christmas day works - it doesn''t give either the children or the parent (and extended family) enough proper time to enjoy the usual festivities and family traditions. My ex and I did try this for a couple of years, but the children didn''t enjoy it, and it was they who said (at just 9 and 4) they didn''t want to be passed about like a parcel on Christmas Day any-more; so we alternated Christmas, which worked much better for everyone. Each family was able to enjoy a whole Christmas Day with the children, even if it wasn''t on the 25th December.