I went on a
DCL Mediterranean Cruise back in 2007. I joined a Cruise Meet Thread here on the DIS and some of us got together and booked some private tours. There were three families on each tour (mix/match), and we were 10-11. We used this company, and were able to tailor our tours. You might want to check them out:
http://www.limoinrome.com/
What I liked is that the driver would take us someplace and a local guide would give us a tour. We were able to visit and tour (without waiting in line) the Vatican Museum, Sistine Chapel, St. Peter's Basilica, the Coliseum (again without waiting in line), have lunch at a local pizzeria, have gelato from a big gelato shop, tour the Pantheon (loved it), and visit Trevi Fountain. We did a lot in just one day. We used the same company in Naples to visit Pompeii (loved it), drive along the Amalfi Coast, eat in a restaurant high on the hill overlooking the Mediterranean, visit Positano, and stop in Sorrento (for a little bit).
(I had to go back in my emails to find the email from the company.)
Here's what his email said: