I haven't agreed much with Mr. Dent lately but I have to on this point. Its stupid to have a black Johnny and white Sue and just expect the audience to just buy that without addressing the elephant in the room. Its not worth the hassle as that immediately draws attention to something that people shouldn't be focusing on. When adapting these franchises to the big screen, you need to keep things as simple for the mainstream audience and going through all these hoops to try and sell 2 characters who are clearly of a different race as full blood siblings is an unnecessary complication. The simplest route would be to just have them adopted or to make them the same race.