I don't know a lot of the golf swing, but I'll try to apply what I've learned here so far...
He has very little lower body action, and I think that's a big reason he is so steep at A4 and comes over the top. In the end, the biggest issue I think is Key #2. But first, I think he needs to work on the backswing to get in a better position at A4.
My recommendation would be to get more flex in the lead knee and maybe a little less flex in the trail knee to get the hips a little more tilted. Second, the trail elbow is really high, so I think I would have him hit some shots with a head cover under his trail arm. Hopefully all of this will get him in a better position at A4 to come into the ball from the inside, instead of over the top.
Like I said before, Key #2 appears to be the biggest issue. At A7, he appears to have more weight on the trail foot, and the heel is firmly planted. Shoulders are also really flat, and I think it's probably just a result of the over the top move; he's having to clear his left should around, instead of it rotating up and around.
In fact, both feet are still planted at A9.5. Not until the very end of the swing does he pick up the trail heel, but it's obviously a forced move.
As far as drills for Key #2, I think rolling the ankles would be the place to start, so that he can get that feeling of feet moving. Once he's comfortable with that, then I think the preset hips drill would be really useful. At this point, having the hips move forward is going to feel really strange, so it's going to be a lot of slow swings to start getting the feeling of weight forward.