How difficult is it to return our rental car to the Termini area instead of the airport in Rome. We will be driving back from Florence to spend the night in Rome before heading home.
Access to Termini is fairly straight forward. Get a good map or GPS. You do not have the same concerns about TZL that you have in Florence.
Easy. Go down the A1 on the east side of the city and turn west on the A24. You'll get dumped on a clear route to Termini and miss the ZTLs.
Have you considered leaving the car in Florence and taking the train for the remainder of your trip?
There are 4 of us and the cost of train tickets does not make it worth it when we have a car. I just did not want to get into a mess with driving into zones that are not allowed.
No problem with that. There is a highway whose terminus is near Roma Termini, beyond any ZTL zone.