Italy - Which cities/areas in 10 days?

The more people you have traveling, the more important I think it is to slow down and focus on a small area. Don't feel you have to do all three major cities on your first trip, and definitely don't add anything! Three days per city is cutting is close already.
Are flights purchased, scoped out (as to what is most likely)?
How many people, ages?
Cinque Terre: If you are into hiking, there are alternatives. If you are not into hiking, there are alternatives. It will eat a tremendous amount of time to get there from Florence or Venice.
Are you interested in renting cars or sticking to train and bus?

Ok, not very helpful, but beyond "Rick's suggestions" (which are a good place to start based from what I've read of his guidebooks), what calls you to Italy? Why did you want to go in the first place? With a larger group, you need to have an idea of everyone's travel interests to try and find balance.

5 total: parents both 69, husband and myself mid 40's and pretty active, and a pretty adventurous pre-teen

My husband and I have been to Italy before and fell in love (Venice, Florence, Rome (which was actually my least favorite)). My parents and my daughter have not been. This will actually be their first visit to Europe in general. I am concerned about too much "city" and crowding for my parents in particular. We all love cooking, food, history, but not necessarily art. Walking for long distances is fine. Hiking for my parents, not so much. Based on the previous response, I think Cinque Terre might be better suited for another time.

Planning to take trains between major cities, but not opposed to driving (or hiring a driver) to do day trips.

Nothing is booked yet and we are fairly flexible about where to start.

If this is your first trip to Italy, I would stick with Venice, Florence and Rome! There are PLENY of things to do and see and numerous day trips that can be added. The first year we went we did a day trip to Cinque Terre. Since we did not take the earliest train from Florence, we were limited on our time. We picked one of the five towns, grabbed some gelato and enjoyed people watching sitting on the rocks. We did not do any other day trips as there was so much to do, see and eat in Rome, Florence and Venice.

Our second trip to Italy we stayed in a few different places....Treviso, then to Milan with a day trip to Lake Como, Florence with a day trip to Chianti and a day trip playing on a Vespa. We stayed in Rome again but took a day trip to Tivoli. Also stayed in Naples for a base but did day trips to Capri, Ischia and Pompeii. That my friend was one crazy trip and I will NEVER cover that much space in 12 days AGAIN.

Personally, for a 10 day trip, I'd skip Venice and do Florence, Siena, and Rome. With more people, everything moves a little slower (as another poster said), so packing up, going to a new place, and getting into a new hotel all takes a bit longer. Those 3 cities are all a little more geographically condensed, so you'll be spending less time travelling, and I think everyone will still enjoy them all.

At this point, I'd delve into some guide books that go into detail about the various regions and consider adding some smaller places--(one) city plus a village is a nice formula! With only five people, you can still get by with one large rental car, if you decide to explore a rural area of Tuscany for example.

3 places in 10 days is smart, I think that gives enough time to get to know a place a little. Since you say you like history but are not so into art I would skip Florence and do Rome, Tuscan hilltown or countryside plus Venice. Are you flying open jaws? That will save time (into Venice out of Rome). What did you not like about Rome? The history is everywhere. Maybe the place you stayed was not good or you found things too crowded? There are ways around that like pre-purchased tickets or tours. It will be hot in July. I would pick a working farm (agritourismo) near Montepulciano or Montalcino with an outdoor pool. If you do cities only you miss the charm of the gorgeous countryside.
Have a fantastic trip!

Would you consider renting a car? I like the idea of starting in Venice and ending in Rome.

Venice - the perfect place to take it slow and get over the jetlag. If you avoid the most popular areas during the day (go to St. Mark's, Rialto Bridge in the early mornings and evenings) it's not too hard to avoid the big crowds. You can take a rowing lesson, which should be great fun, especially for your kid.

Rome - I didn't much like it at first either. There are lots of choices. You don't have to spend hours in the museums. Orthe Colosseum and the Forum, but they are lovely to stroll past and even more so after dark. Visit the gardens. You are likely to see folks playing Bocce and it's interesting to watch, you may even be able to talk your way into trying it. Take a local train to Ostia Antica and walk through 2000 year old Roman streets. It's a half day trip or combine it with a few hours at the nearby beach. Take a food tour.

In between - The Cinque Terre is probably not a good idea, due to extreme over-tourism. If you rent a car, you could stay somewhere rural (some have a pool) in Tuscany or Umbria (Umbria is as scenic as Tuscany, not as popular) and day trip to villages/towns that are not as accessible so maybe not so crowded. Without a car, consider Bologna which is a rail hub (and on the main train route between Venice and Rome). It's get many fewer tourists. You can tour the oldest university in Italy, take day trips to a number of good destinations . . . Modena, Ferrara, Padua and more

For a 10 day trip, I would skip CT and Siena and stick with Venice (3 days), Florence (3 days) and Rome (4 days).
You need way more than 4 days in Rome and you can take the train for the entire trip, no need to rent a car.
Another option is Venice 2 days, Florence 3 days, Rome 5 days.

We went two years ago to Greece with our children, my daughter's husband, and my husband's brother. We are planning a similar trip to Italy next year. We had seven of us but less spread of ages. We stayed three or four nights in every place and that was perfect. It takes more effort to move around with a group.

I would suggest you think about what you want this trip to be and what people will enjoy. I found variety to be really important, especially with a group. For my crew, going to the three main touristed locations in Italy would not work well.

So if I were in your situation, I would consider substituting smaller places for one or even two of the big cities.

I am concerned about too much "city" and crowding for my parents in particular

Since you've been to Venice-Florence-Rome I suggest you think out of the box a little. Since Rick Steves guidebooks aren't written on stone tablets, there's nothing that says you have to do what a large majority of tourists will be doing in July 2020.

You said Rome was your least favorite. On your trip of the trilogy, did anything stand out so much you feel your fellow travelers shouldn't miss? Maybe you could build a trip around that.

I'll offer a thought based on your "too much city" concern. Spend 4 days in Florence. Then, rent a car and stay in a countryside agriturismo in Tuscany. From there, you can make day trips to all the wonderful towns and cities nearby, including Siena. We had been to Venice, Florence, Rome, Assisi before, but on our last trip to Italy we spent the entire time in Tuscany with our home base near Greve. It's an entirely different and charming side of the country.

My parents and my daughter have not been. This will actually be their
first visit to Europe in general.

Hi and welcome to the forum gang, Jessica!

I'm in the Rome/Florence/Venice camp but have your parents and daughter weighed in on what they want to see? It's not at all unusual for these three cities to be on most first-timer lists 'cause of the iconic attractions they've seen the pictures of all of their lives. You may also like Rome a little better the 2nd time around as you'll have already made her acquaintance.

Crowds and the heat will be considerations when planning your days. Both can be managed with some strategic sightseeing that includes some daily "down" time along with visits to the busiest attractions/locations. In Venice, for instance, our posters in-the-know report that crowds pack the San Marco area but you can stroll other areas of the city blissfully mob-free. If you don't overload your daily itinerary with most-visited sites - don't try to do the Colosseum/Forum/Palatine/Vatican Museums in one day! - the crowds and heat will be easier to manage.

If still worried about overload, you could even further reduce your locations to just two locations and take day trips as the spirit moves you? Florence, say, is a very good base for easy day trips to Lucca, Siena, Fiesole, etc. via public transit. You could also do the Cinque Terre from there but if crowds are a concern and hiking is off the table, I'd definitely save it for a different trip with more time, a smaller group to move around, and not smack in the middle of high season!

Some things have likely changed since your last trip to the Holy Trinity (Venice/Florence/Rome). As tourism has greatly increased over the years, more and more crowd controls have been enacted at many of the most-visited attractions. Those usually involve buying timed-entry tickets well before a trip but the whats and hows of that can be a NEW conversation once you've decided where to go/what to see. :O)