Things change. Our own family traditions may seem set in stone, but they aren't. There are always exceptions -- sibs visit in-laws, people go on vacations, grown children can't get home or want to do things with their friends or their own families alone for once, we can't ski Christmas Day because there is no snow or somebody's sick or somebody has to go on a business trip the next day. People don't like change, but that is tough. Change is a part of life. Your family needs to accept that and get over it. "This is what we are doing this year." Lather, rinse, repeat.