Drive or train from Tuscany area to Rome?

While I am a big fan of rail travel and discourage people from driving in Roma, I think your situation would best be served by driving to Roma and dropping off the cars. To go to Firenze, drop the cars, and then pay for 7 train tickets does not make sense in terms of time nor money.

Do pick an easy-to-get-to location for your drop off in Roma. Maybe at Termini, so you are conveniently in Roma yet avoiding the congested center.

Thank you Laurel...and you answered my next question already which was where in Rome would be the best drop point if we go with that option?
I have no interest in driving in Rome so an easy drop off and train/bus into the city would be ideal. If that's Termini, then that's what we'll do!

I think you misunderstood what Laurel wrote.
Termini is not a city outside Rome, it’s the name of Rome’s main train station.

Many of us use a consolidator to rent cars
www.autoeurope.com
www.kemwel.com
Both are part of the same corporate umbrella.
Their best deals are with Europcar or Hertz.
Use the Europcar or Hertz websites (depending on which one you choose) to find the location that is most convenient. Both have at least a dozen offices in Rome.
Termini station is just one location. The Termini car return multistory garage is on via Giolitti at the corner with Via Mamiani, next to the Radisson Blu hotel.

Thank you for the clarification Roberto. I figured it was a terminal or station of some sort.
I just re-read my reply and realize it wasn't very clear. I just meant that we're not interested in driving around extensively in Rome so an easy drop off point would be best. When I bring up the various car rental locations, there are a few that seem to be located in the city center which we'd like to avoid. I will look for one at the train station.

Edit: and thank you for the links! I've looked at europcar but not the other one...will check them out!

If you can drop the car off at Roma Tiburtina, on the outer edge of Roma, you can take the train from there to Roma Termini.

Tiburtina is a very easy drop off, especially if you're coming from Tuscany. I made the mistake of dropping a car, once, at the Europcar Rome Via Veneto City Office thinking I would be closer to our hotel. Never again! That one is a very narrow street with no parking, about one block out of the ZTL. Tiburtino is so close to the autostrada you can't make a mistake. To make things really easy, take a taxi from there to your Rome hotel.

Or at FCO, the airport, and take a flat rate taxi or the dedicated train, Leonardo Express, from FCO to Termini.

Many, many travelers with Hertz rentals drop them off in Orvieto and take the 70 minute local train into Rome Termini. it is all 4 lane highway and expressway from either Florence or Siena and maybe a 90 minutes from Siena..
Orvieto is also a great one night stop with great hotels and it is a very popular hilltown.
The Hertz location is across the parking lot from the train station--easily dealt with.

I have picked up a car at Roma Termini station with no problem, so if I were staying near Termini, I might indeed return one there. (Full disclosure: I picked up there because I misremembered advice to pick up at Tiburtina.) Or you could take two taxis to your hotel.

But last month, since my Rome hotel was in the Trastevere neighborhood, and neither large train station seemed to add any convenience, I returned the car to Fiumicino airport. Note that cheap trains from the airport serve more stations in Rome beyond the larger Termini and Tiburtina stations. You can check train schedules to Roma Trastevere, Roma Ostiense, or Roma San Pietro (with a connection), for example, depending on your destination.

In May, when finishing our time in Tuscany, we also returned our car to FCO and then took the Leonardo Express into town. That worked well for us.

Thank you all for the valuable advice. I'm thinking we need to determine where exactly we will be staying in Rome so as to determine the most convenient drop off location. We're looking at Airbnbs all over the place; I just got my Rick Steves Rome 2018 guide today so after I peruse the book, I think I will have a better idea of where we want to stay.