It sounds like you have been taken for granted Sinking,and I well know what it is like in the family when the culture is patriarchial and the male sibling get treated like king whereas the females are used and put upon or ignored.You need to put your foot down cos it sounds like in your family there are power struggles and everybody is expected to know their place.It seems like you are expected to do certain things and there would be an almighty row if you refused to tow the line.It isn't fair to you at all.I lived this in the past myself it is as if I didn't exist or matter and it made me very unhappy.I walked out on that family situation,I didn't want to be used and abused anymore,I had a sister used and abused me something terrible.I never married cos of my experience of family life growing up.
I am sorry for the way you are treated,go off on your own and redeem what is left of xmas for yourself is my advice!