Brothers share a link that is unique and special. Same DNA, same familial backgrounds, quirks, talents, and sometimes musical taste. They can also argue, get physical, try to overpower one another, and hold grudges over years that are hard to explain, even to people in their immediate families. Bands come preloaded with the same traits, and grow to feel like a family of brothers, and sometimes sisters.
It makes sense that a band featuring brothers in its lineup would be a recipe for disaster in some cases, but not always. Take the Abbotts, Dimebag Darrell and Vinnie Paul. They swore allegiance to themselves their whole lives, in Pantera and the bands that came after that one's demise, until Dimebag was shot and killed onstage in 2004.
For the brothers that do get along, they have the advantage of being a ruling majority in most bands, or banding together in a duo to call the shots. Most people see Van Halen as a tool of Eddie and Alex, with singers and bassists just hired guns. True, the boys do have a trove of tracks they have recorded together, that sometimes leak online.