A 303 page Chess Teaching Manual by IM Ton O’Donnell is available from the Clarksville (Canada) Chess Club HERE. This giant manual is designed for adults to use in teaching children how to play chess starting from the very beginning. Each lesson is designed to take about 10 minutes and also includes exercise sheets designed to reinforce the lessons. I can see no reason why this manual couldn’t be used to teach adults also.
The Rockford Illinois Chess Club also has a lot of free material available designed to teach beginners as does Professor Chess. While you’re at Professor Chess you might like to try their "Recon64" page where you can try to guess the next move in some master games. In order to gain full access to all of their resources individuals have to pay $10 per year but they also offer a lot of free downloadable material suitable for small chess groups. Worth a look if you are in a teaching situation.