If you start shooting this stuff now and go back and get the relevant interviews after it either goes to absolute shit or turns into a heartwarming tale of perseverance,
you could seriously be on to something.
Right now I'd go for fly-on-the-wall until they get used to having you around with a camera and then you can start asking questions.
Shoot in HD, be there for family reunions, the birth, etc. and just keep rolling.
Worry about the story when all is said and done (no matter which way it goes) and you'll end up with something that people will want to watch.
I know I would.
Then again, I just watched the documentary about the guy who died from being fucked by a horse, so maybe you shouldn't listen to me.