One of the big names in chair yoga is Lakshmi Voelker. I think she started more than 30 years ago. You could look at her ‘get fit where you sit’ dvd and see if it would work for you.
Also you might look at the book ‘Easy Does it Yoga’
I personally feel that seniors benefit more from doing yoga in a class. Social engagement is so important for continued brain health and quality of life. In addition a skilled teacher can help them make modifications as they need it, and that attention (which is a part of yoga that makes it what it is) is even more important in this group where there are generally more limitations and health issues than in other groups. There is also the fact that falls are a big issue in this group. And if someone with a balance issue falls and fractures something at home with their DVD it would not be good.