I think you already got some great advise, but let me add some points that come to my mind:
- The hint in regard to the various brands and models is imo very valid and it's good that you already downloaded some manuals. In your position I would probably try to get for an hour to some shop and gain first hand experience on several models of the two, three major brands. And if you have a way to get in touch with the participants now, then think about a 'happy to meet you folks in just a few days' eMail. There I would also include the kind request that they bring their own manuals, in case they think they will need help with their cams.
- One of the best advises I got from a trainer was to always criticize in a positive way or at least in a 3:1 ratio.
- Also you can always help them by asking their opinion: "What do you think is the best aspect of your picture?" "What would you think could have been done better?"
- While you own them and you should be the leader it doesn't means that you can't throw in some anecdotes of moments where you struggled or failed.
- Take a moment and try to google up some 'In my bag' posts of wedding photographers. I' m not talking about the gear they use but of the stuff they bring to a wedding for the bride, the groom and the guests. A lot of these things would be things I would bring too. E.g. some headache-pills, some tissue, insect repellent, some lens cleaning microfiber (there are so cheap ones, that you can hand them as a present, who cares for 1 buck?), some band-aides, one or two multi-outlet powerstrips, maybe one or two spare plug-adapters, ......... and many other things.
If you are not only the teacher but also the problem-solver and helpful hand, it will give you a much better standing with your group and there will certainly be quite a lot of "I forgot ...", "I ran out of ...", "I need ..." moments.
- Don't let their gear fool you! Within the group of well settled people is a significant amount of Noobs with high[est] quality gear. Ppl I met: Mrs. Dr. med who ownes a 1Dx, some nice L glass and shoots on high-ISO in P-Mode pics of her newborn. Or Mr. Executive who started with a 1DsIII, then switched to D3 and after establishing that it's just a piece of junk finally(?) settled for a Phase to shoot his holiday snapshots.
- On the first day, during the greeting-session, ask them what they expect from the tour, what they would like to learn.
- Half way into the time you could ask them how satisfied they are and towards the end have a ups-and-downs session. What they liked with you, what don't.
- Finally, if you ask me what to teach them there would be some positions on my list, marked in red:
-- A good picture creates emotion in the person looking at it; a bad picture only revives memories an the person that took that picture.
-- 'Only show your best.' Rather show 10 good pictures instead of torturing your friend,guest,whoever with 100 bad or mediocre pictures.
-- How to hold a camera
-- Portrait orientation is not only for portraits (or landscape sometimes sucks.)
-- Why a tripod is not an obsolete piece of equipment and why the $$$ for a better one are a good investment
Hope at least some points were useful for you.