OK here are my observations. The posture is pretty good with good knee flex and a nice staright back. Might be the camera angle but it looked like the feet and shoulders were all aiming left. The takeaway is a little flat and that is causing him to lift at the top of the backswing. This means his head position has risen laterally and he has to compensate by dipping in towards the ball.
It looked like it was a pull left and that seemed to be caused by having to get plenty of hand action to compensate for the lateral movement and to bring the clubhead back to square. Too much as in this case will lead to hooks and pulls.
What does your brother play off. There are plaenty of positives to take from that action. I have suffered from similar problems and he needs to focus on a shorter swing and get the takeaway a tad more upright. His left arm needs to come back more across his chest as opposed to inside.
I'm not a swing guru but that is how I see it but I'm sure wiser heads (realgolfer - Dave where are you?) will put you right.
I think he is too stiff and needs to stand closer to the ball, this will fix his stoop like posture. Id also wager he will hit the ball longer too. He has a good tempo though, hes not trying to murder the ball before he has even made his backswing.
What I suggest he does at the range is put a club down and work on his alignment. It will probably feel that he is aiming way right but make sure his feet, hips and shulders are all parallel with the target line. Get him to check (you can help with this) that there is a straight line from his shoulder down past his knee and into the ball of his foot (hold a club shaft straight down from the right shoulder and check these points).
I think once he has got use to aiming straight it will automatically allow him to take the club away wider as opposed to inside and will stop the lateral head movement and the need to compensate with the hands.
I think he has a pretty good swing for that handicap and there is potential to get him down to low teens at least.
To me there isnt an awful lot wrong with this swing that cannot be cured with minor adjustment. I agree with the detailed comments so far, especially the stiffness point. You dont want to be jelly but you dont want to be as rigid as a corpse.
It's not that bad a swing at all. Hands are too far from the body and this also causes the lean over. Move the ball closer and this will sort the problem. Hard to see from the footage but the grip looked strong to me which creates a bit more of a flatter swing.
It didn't look bad at all. I would agree he needs to stand a little closer to the ball. A clenched fist in between the club and his groin for irons..one and a half fists for driver. I'd also get him to think about high hands on follow through.
PS. The pose should come natural to the swing, not as an after thought.
I have already commented on the flaws I saw but I agree with realgolfer. There is plenty of talent and a few long game lessons and maybe get the short game checked as well and LOW single figures next year