Paulie was a soldier in Tony's dad's crew.
Silvio has been a family friend, associate and possibly soldier since the early days as well, having ran clubs before the Bing.
Eugene (the rat) and Tony played on the same sports team when they were young.
Christopher, of course, grew up with Tony and was like a little brother, as Tony watched over him when Chris' dad Dickie was murdered.
Ralphie was a young hoodlum with Tony in the days before they became made guys.
Bobby's dad was a soldier under Boss DiMeo and probably had been in Junior's crew, since it is Bobby who takes care of Junior in his old age. Tony's dad had been a soldier and then captain. So both Tony and Bobby grew up in the business and likely acquaintances.
Vito was related by marriage to Jackie Aprile Sr. and cousin to Jackie Jr. (who he later whacks).
Carlo, Patsy or any of the others? I don't know the backstories.