The problem you're likely running into is that when your hitters land with their stride foot, their hips are continuing to move forward some prior to rotating. This causes all sorts of issues, one being that they will have a tough time keeping their hands inside and extend through the strike zone. Rather, they will cast the hands away from the body and sweep through the strike zone (the second problem you mentioned).
I'm going to post an article I wrote with some clips in it for you to have a look at. The article doesn't pertain to your question, but the clips can help illustrate.
Towards the bottom of the page you'll find the clips. Watch what happens to each hitter the moment their stride foot hits the ground. You'll see the hips open. Many young hitters have trouble with this and will let their hips slide forward after that foot hits the ground. Even if they don't stride many move the weight towards the front foot without rotating.
MLB Clips to watch bottom of page Here is a clip of me teaching how to help athletes feel how to control their weight transfer so that they are using their full potential of their lower half. Begin at the 1:08 mark -
Hitting Drill ClipOnce you tackle this problem then you can work on that extension.
Good luck!
Nate