I'm the third of four, having a half sister and bro, 8yrs and 5yrs older. Their mother died when they were tiny. I have a brother 2yrs younger. I don't see much of any of them as we live so far away. My younger brother keeps himself apart from us all, I haven't seen him for years and years, maybe 2002. He was my mum's favourite. He doesn't have a partner or children.
My older bro I see now and then but he doesn't keep in touch and after years of trying, I can't bothered anymore myself. I always did and still do adore my sister. She has been quite ill in recent years and that fills me with fear. I am in contact with her children and their families, which is lovely.
My parents were only children, so I had no aunts or uncles and just one grandparent who lived with us. I think I felt quite lost amongst so many of us, though, and the competing demands on my mother's attention.
Oddly enough I was talking today to a friend who is an only child, married to a chap who is also an only. She said their upbringings were chalk and cheese even though they lived in the same town. Her parents made their house a home and welcomed any-and-everyone into it, it was always filled with people and busyness so she didn't feel lonely. Her dh's parents were the polar opposite. No one stepped over their threshold without very good reason and he was never allowed to bring friends home or anything. In consequence he had a lonely childhood.