On Canyoneering101.com you will find the following knots which I have deemed the "essentials". They are easy enough that everyone in your group should be able to learn (aka memorize) them without too much difficulty.
Knowing these knots will give a solid technical skill foundation. For re-emphasis, that's what the purpose is of this website.
There are more knots that you could ever possibly know, and knowing 40 of them won't help you if you can't remember how to tie 10 of them precisely.
Essential Canyonering Knots:
You will find these on the Menu, under "Canyoneering Knots". Each of them deserve their own page.
They contain step-by-step pictures on how to tie them, a video narration, and a .GIF format so that you don't have to keep pressing stop and play as you go along.