Likely what happens, in this universe where Keshin and Joanne exist, is that the condition they have is one of those fatal diseases that's supposed to kill you off in infancy or disable you completely. Even on the off chance that a sufferer finds out about the "energy discharge" trick and prolongs their life a bit longer, the results would so alienate their caretakers that the kid wouldn't last long. When you put this situation in perspective, despite Joanne's bitterness she had some truly resilient and decent human beings as parents. But people can only take so much.
If Keshin is able to negotiate a one-time use of the Escafil device for the duo, they may feel deeply indebted to the ship and crew and become fiercely loyal to Ossanlin's goals. Or their old, selfish, cruel habits may catch up to them despite the crew's benevolence. We shall have to see how it all turns out. <3
