Embed YouTube Videos with start/stop

Hi
I need help making a 50 line script work properly.

I want to show up to 6 videos per page, initially showing YouTube thumbnail images only. The video starts when the thumbnail is clicked.

I have just about managed it but the initial thumbnail shows too small.

I have prepared 3 pages to get you up to speed quickly.
1. https://www.scottish-country-dancing-dictionary.com/video/youtube-embed-A.html with start/stop, very slow to load, no thumbnails.
2. https://www.scottish-country-dancing-dictionary.com/video/youtube-embed-B.html without start/stop, fast to load, with thumbnails.
3.https://www.scottish-country-dancing-dictionary.com/video/youtube-embed-C.html with start/stop, fast to load, with thumbnails, placeholder image not fullsize.