So we can do it a number of ways:

1. This page can be password protected with images and description of dance that links back to youtube. Once someone had the you tube link, they would be able to share it with others.
2. We can create the video and share it on youtube, but only the person with the link could watch (of course, if someone shared the link.... back to square one.  Anyway, it would look like this:

https://youtu.be/pO49d6OUEK8

The more I play with it, the more I think you probably want to do it this way:

• let's organize a youtube channel with thought to growth (adding lessons and also private videos that might always be for one person)
• lay out the page on your site.  It would look like above (we can play with sizes). A thumbnail of lesson 1 of this, lesson 2 of this, and then lessons 1 and 2 of that.
• People click on the thumbnail and it takes them to the youtube video

The problem is that, while people would initially get the video through the site, they could then share it.  Not sure there is a way around that, but I'll look around at other sites.