Yesterday I visited my grandfather and my grandmother. Separately, they're from different sides of the family.
My grandfather has a family tree on his wall which my mother updates regularly (last update, 15th December). At the last count he had 25 grandchildren and 38 great-grandchildren, which is why he needs a reminder. On 1st January every year he sits down and writes out all the birthday cards, with the dates written in pencil under where the stamp will go, and arranges them in date order, month by month, so he doesn't forget.
My grandmother, on the other hand, has three grandchildren, and that's it. (And she's from the Irish-Catholic side of the family!)
The reason my grandfather has so many descendants is partly because he has stepchildren, and some of his children/ grandchildren have stepchildren too. Technically he's not my "real" grandfather, he married my grandmother nearly 40 years ago, after she was widowed, but he's definitely "family". Whereas my grandmother is my "real" grandmother but I didn't meet her until 10 or 15 years ago, and don't really know her that well.
I don't know quite where I'm going with this, other than to say, families are sometimes messy... I have five half-sisters but they're just "my sisters" to me. The two nephews I was with last night have a stepbrother and two half-brothers, but if you asked they'd each say they're one of "five brothers". Perhaps we've lost out from not having grown up in 'nuclear' families, but I think we've gained an awful lot too.