Let me touch in on your questions.

When flexing the thoracic spine the shoulders protract. Protraction is a down , out and forward motion of the scapular. There’s no elevation in protraction. When we add elevation, we usually go to far forward and disconnect from the Serratus Anterior and lower trapeze  that drive the organized scapular motion. Usually because people are tighter and more activated in there upper traps and levators and weaker in the Serratus a. and low traps. 

They need to slow down and have a clear image of the movement and manual feedback really helps.

2. The rotation with lateral flexion is minimal and more in the mid-thoracic at the apex of the curve. It’s not a big visible rotation. Just imagining and allowing a slight rotation in the same direction as the side bend is useful. To encourage it, take the front low ribs in on the side your bending towards.

Thanks again for your message and keep enjoying the classes and tutorials!!👊🙏