I don’t know any of my cousin’s cousins. I have a lot of cousins, too. I don’t think it’s weird to not know them.
I came from a large family with a large extended family. There just wasn’t room to have an extra “side” at a family gathering. You either had mom’s family or dad’s, never both.
To this day I find mixed family gatherings weird and uncomfortable. I won’t attend parties at my brother’s home when he tries to host his family and his wife’s family at the same time. His house is small and I don’t want to be crammed into it with a bunch of people I don’t know, don’t want to know, and have nothing in common with. (It doesn’t help that most of them are socially awkward, including my SIL.)
I have one first cousin. Her father…my uncle by marriage…has a sister. I met the sister for the first time when I was in my late 20s, at my uncle’s mother’s funeral (I had never met his mother either). I also met her three kids (my first cousin’s first cousins) at that funeral and as it turned out, I already had met two of them completely independently of any family.
Of course we all live within about 5 miles of each other, so it’s not all that surprising that our paths had crossed.
I know some of my cousin’s cousins but by no means all of them. I know my Uncle S. has only the one brother-in-law and I met his three (or was it four?) daughters at Christmas a couple of years ago. Auntie S.'s in-laws used to invite us along to some of their family events and we all shared Christmas a number of times so I know the two kids of her sister-in-law. Auntie J’s got a nephew by marriage who is somewhat famous (infamous?) in his profession and I dimly recall meeting him and his sister when we were all young, but I can’t recall the kids of the rest of her in-laws (bigger family).
While talking family trees with my great aunt, I discovered that my ex’s cousins and my dad’s cousins shared a mutual set of cousins. That was a surprise.
I have one uncle on my father’s side, who has three kids. They have three cousins on their other side. We used to do Thanksgiving all together, before the cousins’ cousins moved abroad and my aunt and uncle divorced, so sure, I knew them.
I have 71 first cousins on my mother’s side; about 40 of us are married, with well over 100 kids and counting. While I know a few of my cousins’ cousins on that side for one reason or another, hell no I don’t know the vast majority of them.
My mother had 12 siblings, many of whom went on to have over 5 kids. Those Aunts and Uncles are spread out across Canada and the US. Many cousins I haven’t met, many I met only once or twice as children. I could walk right by them on the street and not know, quite literally. I’m not even sure if I could name all my Aunts and Uncle’s, definitely not their spouses, who’s still living, who’s gone now.
Anyhow, I have tons of first cousins that I have never met. My mom isn’t close to her family, and so I’ve only met (once, when I was 8) four of the at least 30 on her side. One of them was named Gretchen. That’s all I know.