Homeless people die everytime someone makes a thread like this...
Let me put it this way; Square would be making a huge mistake if they ever went down the "BHK and Sora are brothers" road, because firstly, they've had to explain it all, then fans would want prequels about how they got seperated, secondly they may look the same, but they are not identical in anyway what so ever, I don't even think they look like each other.
Also, the whole family twist has been so overdone since Star Wars. I would seriously be disappointed (Sp?) if they even went there....I mean, I've seen it done so many times, it has actually become boring...I watched an episode of Shaman King the other night, and they had the whole "I'm your evil 10000000000000000000 year old twin, and I wish to kill you..." and I sat there and thought "What the hell? Where do they get this pile of crap?"
So overall, Square would actually kill the plot if they have done that.....