sunnymonkey

I like vincezo's idea of splitting the trip planning of three cities amongst the three of you. If you aren't familiar with the cities, it can take quite a bit of leg work to do so, but you learn so much in the process.

As others said, a fully guided tour can definitely get quite expensive. Best of both worlds would be to find local tour guides for specific attractions or "for the day" so you can get the most out of it.

Venice was shockingly expensive for housing (in May which is considered high season), but we found a great B&B on booking.com that was reasonably priced and reasonably located: B&B Al Palazzetto.

In Rome, we stayed near the Vatican but also near a metro stop so it was easier to get around. It was more reasonably priced than staying more centrally, but we were also looking pretty late in the game so if you are starting to look now, you may find better rates. We stayed at B&B called The Upper Suites (also found on booking.com). I would recommend them but I think they only have doubles.