Wow, lots of great advice.
There were two reasons I wasn't going to use a flash. I gave up on it years ago because I just couldn't decent results and never discovered until last night that I have an automatic flash that will cable to the lenses. There will be 3 groups of 8-12 people and it should be powerful enough to light them up, but probably not if the whole bunch get together. So now it looks like it will happen in the shade with fill flash and I'll have to rope a coworker into donating his pickup truck to get the camera a little higher.
Originally this was just going to be an opportunity for me to get the group together and snap a couple of shots with my new toy, but it's taken on a life of its own. With all this help, I got a feeling the results are going to be a whole lot better.