I just took a look. His hips are fine. If anyhting, he doesn't get them opened up enough by footstrike. His problem is with the upperbody. The shoulders should be completely closed at footstrike. He's opening them up almost halfway by the time his landing foot hits. I'd leave the lower body alone and have him work on waiting much longer before starting the rotation in his shoulders. One possible way to do this is with a later handbreak. I fix this in a more dramatic way that I don't recommend because it gets a lot of criticism. My own son brings the ball completely behind his back. I did this because he just wasn't comfortable with a later hand break.
As to the hips. The traditional teach is that the hips should stay closed as long as possible in order to gain rotational momentum. However, there is nothing that backs this up. I've come to believe that the important thing is that, at footstrike the hips be open, the shoulders be closed and the arm be in full cock position. How you get there doesn't matter and any rotational momentum gained from twisting the hips at the last minute to reach this position is momentum in an unused direction.