With Christmas coming up, the BF and I have decided to adjust our plans from the usual. Typically we spend Christmas Eve with my extended family (anywhere from 20-35 people depending on who shows, who brings a friend/coworker/neighbor/etc., it's pretty casual and fun), and Christmas Day with the immediate family (opening gifts and having a small brunch with anywhere from 4-8 of us).
This year we've been planning on spending the 25th with our other partners and possibly some other close friends, all of whom we do consider close family to us. I know it's typical for, say, married couples to alternate holidays with one partners' family one year and the other partner on the off years. This is what my sister and her husband do, since both our parents and his live locally (my BF's family is out of state). Among the family, it's just accepted that that is what happens when you're married--"custody" of holidays is shared and to my understanding this is considered acceptable etiquette.
What I'm not clear on is, what is the etiquette when doing holiday "who gets what holiday" when dealing with non-relatives or non-traditional relationships?