Any Supernatural fans out there??
Here's what I thought: John = Bill, Dean = Zak (I know, bare with me), Sam = Lee.
Carollane Adama is killed by a humanoid cylon when her son Zak is just a baby. Bill discovers the truth, that there are cylons that look like humans hiding amongst them, but nobody believes him. He leaves the fleet (or maybe he already left by then, John is an ex-marine after a war, after all), grabs his sons and starts hunting the cylons. He trains his sons from an early age.
Lee is tired of the life on the road and leaves his brother and father to go to law school. When Bill disappears on a hunt, tho, Zak has to convince him to get back on the job.
I know, I know, Dean is the older brother, but I don't think he is Lee on this one. Lee is most definetly Sam = wannabe lawyer that ends up being forced to follow his dad's carreer choice, boy scout that plays by the rules and crappy, crappy taste in women. :P I think with a little tweaking we can make Zak a good Dean.
Bonus point if you manage to put Romo/Crowley in it. (And, seriously, if I could be anyone in the planet, I'd be Mark Sheppard. He managed to work with all my scifi crushes: Jensen Ackles, Jaime Bamber and Adam Baldwin. Seriously.)