Any help would be great
He shifts his weight back towards 2B before lifting his knee and going forward. This create unnecessary movement that can affect control and it gives baserunners a jump. The cause is that he sets up on the rubber with his feet too far apart. Have him narrow his feet position until he can lift and go forward only.
I Recently noticed that my 10 year was leaving his glove arm down rather than tucking it to his shoulder as he finished his pitch - I think your son might be doing same a bit. A very simple fix that produced nice result immediately - Big improvement in control and power - release point came forward so tendency to throw pitches up and out of zone reduced significantly. Power went up too as result.
I would also like to see him control his glove side better. He begins to extend the GS then kind of leaves it down in front. He should work to get equal and opposite, leading with the GS will help his shoulders stay closed off longer. Then bring his chest to the glove as his shoulders open and fire instead of just tucking it away.