What might be some differences in the way we move or the muscles involved in the narrow and wider stance in the side split series?

Thank you for your comment and excellent question Manasa Kannan - I do cover the answer to this while demonstrating the exercise. I always try to include cues for body mechanics in my teaching to better inform both clients and fellow teachers of what muscles should and shouldn't be working, as well as, planes of motion.  

Laura Thank you so much for your reply! I rewatched the video and got what I was missing. I guess I was really mesmerised by the exercises and your teaching method and missed on the cues you gave on this particular exercise :)

Manasa Kannan my pleasure! Feel free to reach out with any additional questions. I'm happy to hear you enjoyed this class :)