I'm not going on that tour but just had a comment. We'll be in Sorrento next spring with another couple and we want to do the Rick Steves shared tour to Capri with Mondo Guide too. I emailed the company to ask a little more about how this works. They did confirm that if advance sign ups don't result in meeting the minimum, but those who DO sign up are willing to cover the cost as if they had gotten the minimum, the tour will be taken. So the four of us are satisfied that we'll be able to go because we're willing to pay for the missing two people if it comes down to that. The cost seems quite reasonable compared to other tour companies who offer day trips to Capri. I'm sure some people in your tour group will want to do this with you, even if they don't see this post and don't learn about it until your tour starts. Hopefully it won't be full, leaving them disappointed they didn't learn about it earlier.