Live together as brother and sister, work til you have enough money, move to America, change identity and marry.
It happens all the time, it isn't as insurmountable an obstacle as you may think.
Related way too much to the kind of loneliness Riku and Sora felt, my instinct would be to fight tooth and nail to stay together, incest doesn't even enter into the equation, I chose her route because I wanted to take care of her, I honestly forgot about romance entirely until it was too late.
I grew up separately from my younger brother, neither of us had particularly happy childhoods, and when we met for the first time again as almost adults, he looked upon me with such hope and admiration. He had built up this image of me in his head of a hero of some sort, someone who could show him the love and true brotherhood he had needed so desperately when things were at their worst.
I felt such incredible horror and shame then, I was no better off and worse yet, had no hope of an older brother to take away that pain when no one else cared, I had fallen to despair early. I couldn't help him, I didn't now how to love any better than he did.
I had hoped to meet the brother that turned out alright, that could tell me of his good memories, tell me about the car he had eyes on or the girlfriend he swore he would marry.
I broke when I realized that he had sought a salvation in me I could not offer, that our meeting again after all this time would just be another wound to bleed him. It didn't take him long to see me as I was, a wretched soul in the pit with him. I tried to pretend, to act the part, but every day I could see less and less hope in him.
He eventually cut off his final roots, just like I had so long ago, and we once again went like the butterflies, living on if only for the hope that one day the winds would finally take us to a place of happiness.
Not everything ends well, but I like the stories people tell of when things get better, it makes me glad to be able to pretend, even if only for a short while, that it's just me down here, that up above where the birds sing and the sun shines, everyone can find a place in the world to feel at home.
Maybe my brother is up there, with his wife and a kid on the way, pretending that I'm not here. That would make me happy.