Christmas Drama issues with my family!?

I am in my late twenties and my parents usually throw the "traditional" Italian X-Mas eve dinner. I am now engaged (1 yr on Xmas Day this year '10). And my older sister (mid thirties) is married for 2 yrs. I was told by my family ( in the summer) that they don't care where we go. I told my family 2 weeks ago I would like to spend it (X-Mas Eve) with my fiance and her family this year and then spend X-Mas day with them. Well my parents flipped the $&!? out!! They started screaming and yeling saying that they were invited to my estranged Uncles house on X-Mas day and we (my sister and I) wont see them until Dec 26th not even for breakfast or gifts on the 25th. I am heart broken and I can't stop getting emotional over it and my parents started the whole guilt trip saying they are the last to know everything blah blah blah blah. Am I wrong for telling to grow up I mean these people are in their 50's for crying out loud. They don't seem to realize that family dynamics and things change. I do not know what to do.....any advice out there?