I agree with every point made by renegade there. Yet, once they decided to shoehorn a brother in there ( pretty cheap device, really ) they could have fit that within the overarching plot a bit more ellegantly.
-Do you really trust this Sullivan guy Nate?
-Yeah, I've trusted my life to him many times and he never betraied me.
-but you only hang out with fim for what? 6 months? A year? When you were 13...
-It were 18 months, and I was 15. But yeah, I got back together with him after I thought you had died, and have been working with him ever since.
Boom, done. How hard was this? I'd even guess something of that sort was drafted at some point, but they decided they'd rather leave that open for further games and material to work with. I disagree with that decision though. As Renegate put it, the whole apearance of a never before mentioned drake brother is way too contrived to leave such nasty question marks unadressed like this. There is still a bunch of other parts of these characters lives open to imagination. They should have given more care to at least this one.