Learn to turn the barrel with hands and learn to resist turning forward with the back. Rear leg turns you forward. But, to start learn to make first move turning barrel with hands.
Forward with the back ?
For the front shoulder I like the one handed drill, usually with a stubby bat. When swinging with the front hand have them focus on keeping that front shoulder in all the way through. It helps sometimes if they place their back hand on their front shoulder.Front shoulder flying off or lack of separation in a young hitter