I think you need to clarify off the bat that both players would be good players.
Obviously pairing a good player with a bad player doesn't work, my assumption is you're asking more specifically about tendencies and chemistry and if being as close as a brother to another person could help in complimenting a line.
I think it would certainly make it easier to adapt playing with your brother. You have a good idea of how he plays and what are his strenghts and weaknesses. You don't need to spend time learning how he plays and how he moves around the ice, what he can and cannot do. There's more transparency, better communication on the ice, more honesty, instinctually you would know more about his positioning and movement around the ice. You've known this person for years and watched this person play hockey since you were a kid so it's completely normal. Just like guys that play a long time together learn about their tendencies and all. I think it's certainly an advantage but it's impossible to quantify and it rarely ever happens.