We just got back from a cruise last month where we did this. It was a lot of fun!
My husband and I opted to share a jet ski (with him driving). I wanted to be able to take pictures while we were going which you obviously can't do if you're operating the watercraft. So, I can't personally speak to how tired people's hands got, but I believe that's why we paused in the middle (to give people's grips a break). We skirted around the island and out to a very small island where we beached the jet skis and just waded in the water for a bit. It was absolutely gorgeous out there and we even had a stingray come swim around us.
There was a definitely a divide in the skill/comfort level of the people in our group. The fastest people would end up at the front and be guided through doing some extra loops while the slower people caught up to the group. It is follow-the-leader style the whole time.
My only tip is if you do it, don't trust the flimsy waterproof phone lanyards you might bring to the pool. I used mine and at one point the part holding the phone unhooked from the lanyard because the cheap plastic clip inverted. Luckily I had the camera pinned down in my lap so I didn't lose my phone but that's definitely something I'd do differently next time!
