Unlike many families my family celebrates Christmas with really really a lot of our family. This past year there were about 29 people at my Grandfather's house in the week around Christmas. I know what you're thinking: how does that work?
It's actually pretty simple. First, we have a spreadsheet so we know who's coming and who's not, and who's cooking dinner each night. While most people come out for the entire break, a lot of people only stay part of the time. And families who live closer to my Grandpa's house typically either celebrate Christmas Day at my Grandfather's or go home to celebrate with other family.
When people sleep they typically either sleep in one of the rooms at my Grandfather's house, or with another relative close by. It helps that there are five different houses in the area with our family living in them that people can sleep in.
We have many traditions that we do during this time, including making jiaotze (Chinese dumplings consisting of typically meat or beans, and cabbage).
Also, on Christmas Eve, people gather in the living room while my aunt Alice reads a chapter (Dulce Domum) from Wind in the Willows. Afterwards, everyone grabs songbooks and we sing Chistmas Carols together.
You're also probably wondering: how do you do presents with so many people? The answer is stockings. Individual families typically find their own time to have a gift exchange with just their close family, but at my Grandfather's house when we come all together we put out a paper bag for each person. Everyone goes around filling stockings for each other, putting in little gifts and ornaments and things.
On Christmas Day in the afternoon one grownup is generally tasked with the job of keeping the kids busy while the other grownups and any kids old enough to participate go into the living room for the Grab. People put presents under the tree, and each person is assigned a number. By order of numbers, each person goes around choosing either a present from under the tree, or a present someone has opened, stealing it from them. This proceeds, until a present has been stolen two times: the third owner is the final owner. Once a gift is stolen from you you can go back and pick a new present. Each player is required to contribute one present.
Another tradition, but this one only for the grownups, is that typically at one of the grownups houses close by, people come over and they stay up playing board games until about 1am. There are also lots of board games played throughout the day and evenings, by kids and adults, of various difficulty levels.
People also tend to play music together with a range of instruments, ranging from stuff in the strings family, to woodwinds, to free reeds.