I have two older sisters and a twin.
When my family split when I was about 9, I got close to my second oldest sister. She would talk to me as if I were an equal and I really appreciated that.
I didn't get along with my twin at that age but we have gotten along amicably now that we are adults. We don't have that twin bond anymore though.
None of my immediate family have autism or ADHD. My twin needed help with fine motor skills though, and she was held back a year in Grade 1.