We know we made an exception for the Osmonds, but it's simply impossible to separate one of Iowa's Everly Brothers from the other one. They're going onto the list together! The brothers were actually born in different states - Kentucky for Don in 1937, and Illinois for Phil two years later, but after Phil's birth the family moved permanently to Iowa. You can't beat the sound of siblings singing in perfect harmony, and that was the main selling point for the duo.
The Everly Brothers hold the distinction of being in both the Rock and Roll and Country Music Halls of Fame in America, which is a testament to the crossover appeal of their music. They were a significant influence on the Beatles, who used to describe themselves as "The English Everly Brothers" in early interviews. Although both brothers went on to have solo careers apart from each other, they reformed in the 1980s, and played sporadically until Phil's health deteriorated in 2006.