Bane being Bruce's brother is something I can very well see in a Nolan movie.
I would not like such a plot twist. I like to see a series of movies grow organically rather than have shock twists retconned into the story at the last minute. Sandman being the "real" killer of Uncle Ben in Spiderman 3 felt like that and I would feel the same way about a long-lost son here.
Nolan doesn't do these kind of cheap twists. Bane being Bruce's brother would be the very motivation of the movie. I guess. Otherwise it's just a simple Batman vs. unrelated bad guy story.
In Begins it was Ra's, his mentor, and Falcone, who killed his parents.
In Dark Knight it was Two Face, which he put all his hopes in, and Joker, who only appeared because of his own existence as Batman, and who kills his love.
So I could very well see that Bane is there because he is his half brother.