There is a lot of good going on there. If this were a hitter I was working with, I'd quiet down the hand/arm load a bit.
I would agree with calming down all the pre-swing hand/bat movement, and loading a little smoother. My son and I are working on loading more smoothly (2018). Might suggest getting more weight on to the front side (if that makes sense). Looks pretty good in general.
Swing looks really good...hard to tell everything from a tee swing. Think enough is going right that I would primarily focus on getting bigger and stronger. Some slight tweaks will occur after getting stronger.
During this frame,
1. His back heel begins off the ground (comes up too soon) (Notice how his back knee never 'extends')
2. his back elbow drops without significantly turning the bat head rearward (notice that the bat is mostly just sliding down), and his hips are not turning enough. (His back elbow just sorta flops down without much result)
During this frame, his hands are leaving his rear shoulder too soon. The hands should turn with the back shoulder/hips until the back hip is almost fully turned - then the hands should go 'forward'.
1. Try to extend the rear leg more during the stride (keep the back heel down as long as possible) (This will enable him to turn his hips faster/more)
2. Try to keep his hands back until the bat forces his hands away (in frame 2)