Backstory: My parents are divorced and my sister has a different father to me. Each year we alternate for Christmas Eve and Christmas Day. For example last year we were both at our fathers on Christmas Eve and I collected my sister and came in to my mother around 1 o'clock Christmas Day.

Following on from above, this year was meant to be the opposite I.e. we were with my mother for Christmas Eve. About a month ago we had acknowledge that this was the case (as it has been for around 18 years) as she was telling me she got invited to my cousins house and also to her friends house for Christmas Day.

2 weeks ago my sister announced out of nowhere that she was switching because she wanted to be there for when Santa comes for her younger siblings. My Mam and sister then tell me I should rearrange aswell and I refuse because plans have been made and food bought etc. and it was too short notice. They have been guilt tripping me since then, constantly bringing it up, saying how it's better for my younger brother to have me Christmas morning (which i acknowledge as a good idea and may be the case in the next few years) and saying how Christmas isn't going to be good this year.

Yesterday my mother text my father saying that she wanted the switch days and I just spent 30 minutes on the phone with him explaining that it wasn't my idea to switch and that I didn't want to, because he was slightly put out because he thought i didn't want to spend it with them.

I feel guilty that Im "ruining" my mam and sisters plans but I don't think I should be forced to change my pre-arranged plans to accommodate their last minute change.

AITA?

