There is quite a long backstory to this, with regards to lots of unreasonable behaviour, but honestly, I would be here typing all day, so I'll get to the point 
I live with DP, with my 2 dc and his 2 dc that are here half the week and eow. This will be our fourth Xmas together.
Every year, there is a battle over contact with the dc, exw believes that as The Mother, it is her right to have the dc on Xmas Eve and Xmas Day, and DP can have them Boxing Day. There has been a rota in effect for the last couple of years, and this year, it's our turn to have them.
Now, because exw has had a baby a couple of months ago, over the last few weeks, she has trying to tell him that she is having the dc again this year, because it's the baby's first Xmas. DP, as you can imagine, is gutted. He has refused, and the dc, (10 & 13) have said that they want to be here as it's Dad's year and it's not fair.
I suppose my question is - can she actually do this? Can DP refuse to bring them home for Xmas Eve & Xmas Day?
There is nothing legal in place - the rota has worked, for the most part for the last few years, but no court order or anything.
Thanks.