I can't believe this one hasn't been added, knowing its proximity to the Sisters. Anyway, be careful, because all the photos might be considered "family album pics".
Great page with funny info in the overview text. Did some family come through Oregon and just decide to name the mountains after their family or something?
Seems like no one knows. In researching this all I found were comments about people speculating that same question. There are also towns named "Sisters" and "Brothers" nearby. Kinda odd I agree.