In my childhood I knew 3 sets.
Two sets were the children of someone my mom and dad were briefly friends with, and I did really “know” them very well.
One set lived in my neighborhood, and went to my school, but were never in my class, so I’m thinking maybe they were a little younger than me. I wasn’t close friends with them, but sometimes when we were all playing outside they were playing with us.
In adulthood, I worked for years with two different women who had an identical twin, I knew their twins only in the sense that they would drop by the workplace sometimes. I also worked with a man who had an identical twin, but I never met his twin. His twin lived in a different state, but I know they were close, his whole family was very close.
A friend of mine has twin girls, and for years we thought they might be identical. They looked incredibly alike, but now in their late teens it seems more likely they are fraternal. I only see them every few years. They looked so alike as young girls that I’d say they grew up like they were identical. People mistook and mistake them for each other. Their mom dressed each one in certain colors when they were very young to tell them apart. One always in pink or yellow, the other in another color.
I’ve known many more sets of fraternal twins. My experience is that in both cases, fraternal and identical, the siblings are extremely close. I’ve never known twins who have big rifts between them, but I’m guessing that does happen.
My paternal grandparents had twins between my father and his sister. They died shortly after being born; within a few days or weeks they died, I don’t remember exactly. I used to wonder if maybe I would have twins. I have no idea if the babies were fraternal or identical.