^Well, if it helps any, I've read enough of your posts to know that you're definitely not racist or prejudiced in any way.
I didn't find Evans and Alba convincing as siblings either, in the same way that I didn't find Sean Connery, Dustin Hoffman and Matthew Broderick convincing as grandfather, father and (grand)son.
What movie was that?
I'm not sure I buy Shia LaBeouf as Harrison Ford and Karen Allen's son in the fourth Indiana Jones movie either. Although it's not as bad a mismatch as trying to pass off Sean Patrick Flanery as a younger version of Indy himself. River Phoenix was utterly convincing as a younger Ford in Last Crusade
, but Flanery looked and sounded nothing like either of them. (I wonder, if Phoenix hadn't died so young, would he have played Young Indy in the show? He would've been the right age by then, I think.)