If the C8 has tracking - or at least a wedge & clock drive - I'd take that. First time out, most people find it almost impossible to nudge a Dob. Don't know why. Also take a small step stool for Kids to stand on and a Focal reducer (if you have one) and your longest Focal length eyepieces, or at least those easiest to see through (largest Ep, most eye relief).
I have had people who cannot put their eye in the right spot to observe, so the brightest image which is easiest to find is very important. After they've seen it, you can boost the magnification if the target merits it. Also start with the largest brightest objects (moon, Jupiter, Saturn), Albireo , Mizar etc. before you work your way into the faint fuzzies. After they've seen a few things some will be satisfied & leave & others will start to get the hang of eye placement and be prepared to hunt around until they see the target.