Car Rental on a Sunday?

You're brother-in-law is spot on!

You need to check the individual car companies for locations and hours, but for example Europcar (one of the largest in Italy) is open on Sunday morning at the Roma Termini train station location from 8am to 1pm.The airport location is open all day on Sunday from 7am to 12midnight. All other Europcar locations are closed on Sundays.

I checked also Hertz and Avis, and they are also open Sun mornings at Roma Termini and all day at the Airport (all others are closed on Sundays also). However consider that picking up a car at the airport is always more expensive as the daily/weekly rates are higher. Therefore if you decide to rent on a Sunday, I suggest you check the prices at the airport and at Termini station and pick up at the cheapest (certainly the Termini train station). The traffic in the center of Rome on Sundays is not bad at all and from Termini to the GRA (Grande Raccordo Anulare=Grand Ringlike Beltway) is easy.

If you rent through the consolidator Autoeurope.com you can see that Europcar almost always offers the best rates.
Returning the car in Florence is also easy and you don't need to go as far as the airport. Even if you don't want to return at the city center location (via Borgognissanti for practically all companies), there are other options.

Hertz has an easy to reach office on via del Sansovino (for easy reach exit the A1 freeway at FIRENZE SCANDICCI and head to the center of Florence, you will pass in front of Hertz a few km. after the freeway exit).

To return a Europcar rental, the easiest coming from the south is at Via del Gelsomino (corner with Viale del Poggio Imperiale). In this case you would exit the A1 freeway at FIRENZE IMPRUNETA exit and head to the center of Florence. Eventually, after a few km, you will pass in front of the Europcar location on via del Gelsomino.

From those locations you will ask the car rental agents to call a taxi for you to take you to your hotel. The above locations are not in the city center.

Avis only has 2 locations in Florence. The city center (via Borgognissanti) and the airport.

If you return on a Sunday, then the only locations open in Florence are at the city center ( for all companies on via Borgognissanti - Sunday mornings only) or at the airport (all day).

Sounds like you have some good advice.

My advice would be to avoid downtown Florence at all costs. Drop it at the airport. The TLZs in Florence are notorious huge traffic fines.

Since you are coming from the south it's easier to drop at via del Gelsomino (Europcar) or at via del Sansovino (Hertz) rather than the airport.
Coming from the south, to get to the airport would require a big loop around Florence metro area all the way to Firenze Nord and a higher taxi fare to come to the city center.
via Borgognissanti is reachable without incurring into fines, however it requires some knowledge of itinerary within the city.

Great advice

Is there a drop off location near or in Florence near the train station that will get us to the Cinque Terre?

The car rental locations along Borgo Ognissanti are with walking distance to train station.

Here is the address for Hertz- (Avis and others are close by)- you can google it and see how close you are to train station:

Via Borgo Ognissanti, 137R
Firenze, Italy

If you are continuing on to CT and only stopping in Florence to get the train you could simply continue your drive to LaSpezia and drop your car there, then hop on the short train ride to CT. You would then avoid all the worries about Florence.

Drop your car off in LaSpezia instead of Florence. We rented from Hertz and picked up our car in La Spezia, but it's easier to get to from the Autostrada and inexpensive cab ride to the train station. Based on previous research in looking for rental cars, Sunday pickup is not an option in small towns.