Ah, more info. :)
I still think you can skip the whole dystopian intro. At this point, it really is a matter of striping out the unnecessary or redundant... Little things like "sworn enemy" is really just any enemy, no swearing involved. :) "locate and infiltrate" is another one. You can't infiltrate what you haven't already found, so, "infiltrate" is fine.
We do have to figure out who old this brother is though. "... his brother and other children" again makes it sound like the brother is a child, which doesn't seem possible in the scenario described.
What's been mentioned about the inciting incident is important too. If his brother suddenly stumbled home, there would be no need to find him, so, how does he find out he's alive? That's the inciting incident.
"When a government agent which proves his brother has been trapped in a brutal military experiment since his childhood disappearance, he switches sides to help a terror cell rescue him and the next host of captured children."
or, shorter:
"When a government agent discovers his brother has been subjected to brutal military experiments since childhood, he switches sides to help a terrorist cell rescue him and the next host of captured children."
I'm not sure you need the specific what of how he discovers it - if you're pitching live, that can come out in natural discussion, but, somehow, get across that the brother isn't a child, and skin out the useless words, and you should be there.
I think this one sounds like a promising script, best of luck at the ;fest!