Hi Jess -
I am still a little hesitant about the twins and the rigors of this
kind of trip. Are we crazy to consider taking them?
Are you crazy? Heavens no! This forum sees posters all the time who either are taking or have taken children much, much younger than 10: infants and toddlers. They're not only plenty old enough to GO but to do some research prior to the trip...and I highly recommend that ALL of your young people do that. They'll not only be learning about what they'll be seeing but learning how to travel.
Also, having a hand in the plan helps eliminate the boredom factor: if they've chosen some of the attractions they find interesting, and read up on them, they'll be more engaged when they get there. Maybe get some guidebooks and age-appropriate books about Italy from the library and sit down with them as a family? The internet is also loaded with info.
Consider your collective interests when choosing places to go. Florence, for example, is a gold mine for Renaissance art, Rome has a wealth of historic Republican and Imperial-era ruins, and so on. Certain cities also make great bases for day trips to other interesting places. Florence, again, is a great base for a jaunt by train to Pisa and/or Lucca, or by bus to Siena and Fiesole. Rome? Trains to Orvieto or Ostia Antica.
Are you looking for an active holiday or more chill-out time? Some travelers enjoy laid-back stays in country agriturismi (farmhouses) while others prefer hiking in the Dolomites.
Anyway, you get the idea? :O)
I would caution against trying to cover too much ground as moving 7 people of differing ages around a LOT on tight schedules would almost certainly be a recipe for exhaustion and frustration. It would also decrease your valuable sightseeing time. I'd think about picking no more than 3 bases and settling in, doing most of your exploration without a lot of packing up, checking in and out, managing luggage. etc. Summer is also hot and crowded in the most popular tourist locations so you might want to balance city stays with another on the sea (e.g. Sorrentine/Amalfi Coast) or in the northern lakes region, such as Lake Como.
I'd also look at flying open-jaw into one airport and out of another to eliminate backtracking. Just a start....