My parents are highschool sweethearts, and both sides of the family have always gotten along. I think my family is on the smaller side. I have a mom, dad, 1 sister, 1 brother, 2 grandmas, 1 grandpa (other passed away a couple years ago), 1 step grandma, 2 aunts, 1 uncle, and 1 cousin. So the max we will have at a family gathering is 13 people. Everyone lives within about a 60 mile radius, so we get together about once a month for birthdays and holidays. As I got older, I realized not many people have both sides of the family get together like that.
We do have a Christmas tradition where we do things separately with each side of the family. I think it might have started like that because one side wanted to do Christmas eve, and the other wanted to do Christmas lunch, not because they didn't want to spend time together. On Christmas eve, we have dinner and open presents with my Dad's side of the family. Christmas morning after we've done gifts with my immediate family, my Mom's side of the family comes over and does breakfast and presents. Then my Dad's side of the family comes over for lunch and we do lunch with everyone. It's quite crazy.
Another thing that I've found quite funny about my family. My mom's parents got divoriced before I was born, but I never realized they were divoriced until I was probably in 4th or 5th grade. I don't know how to explain it, but I knew they weren't married and that they didn't live together, but I guess since they got along so well and there was never any tension, I never put 2 and 2 together. I talked to my mom and aunt recently about it, and they said that when I was born, my mom and aunt told my grandparents that they were not going to do the whole 2 Christmases and 2 Thanksgivings with them, and if they wanted to see the grand kids and join in the festivities, they were going to have to do it at the same time and act civil. Which they always have.