You'll probably have to drop the car off in a town larger than Campiglia, so I suggest Viterbo with a stop in Tarquinia for its Etruscan museum and tombs.

http://www.flickr.com/photos/mksfca/sets/72157622914974923/show/with/4201819164/

Depending on how much driving/exploring you want to do and how much you want to see Tarquinia, you could also drop the car in Grosseto which has faster, more direct train service to Rome than Viterbo does.

April 25 is a national holiday in Italy, and this year it falls on a Thursday. It creates the possibility of heavy traffic on Friday (and to some extent on Wednesday night as well).

Campiglio Marittima is so close to San Vincenzo, where there is a train station, I would be tempted to take the train from Florence to San Vincenzo and take a taxi from there. The train ride from Firenze is 2.5 hours, with a switch in Pisa. By the time you get a car rental office and do the drive, it is roughly equivalent. Your yoga instructor's office should be able to confirm the availability of taxis at the San Vincenzo station at the likely fare for the 15 minute ride to Campiglio Marittima. (For 3 people with luggage, it will not be much.)

If you don't actually have lodgings in Campiglio Marittima as part of your yoga seminar, consider staying right in San Vincenzo. It is not Italy's most glorious beach town, but you can probably find a nice hotel and a very un-touristy local ambience and good seafood. Look on booking.com.

From San Vincenzo, it is a 3 hour train ride to Rome. It would give you extra time in Rome to just enjoy Rome in addition to sightseeing.

If you'd rather to rent a car to go sightseeing, book early and if you want to see Tarquinia, it makes sense to me to drive there, and then drop off the car at Rome's airport, which is less than an hour's drive south of Tarquinia, and which is open all the time for car rental drop-offs and has train service to Rome every 30 minutes.

Great suggestions!!!!!

Any ideas for my family to stay busy in Campliglia? They are looking for cooking classes or bike rentals.....I did not find much. Is Campligia nice for walkingnaround and finding some good food?

Why not ask people who live there, like the staff at the yoga place you're going to.

It's popular to bike along the Etruscan coast and you could stay in a hotel on the coast that either give bikes to their guests or have ones to rent, and have bike tours

http://www.bikehotelstuscany.com/hotel_en.asp

http://www.bikehotelstuscany.com/scheda_luoghi_en.asp?idArea=41

http://www.turismo.intoscana.it/intoscana2/export/TurismoRTen/sito-TurismoRTen/Contenuti/Itinerari/visualizza_asset.html_338776437.html

Or if you have a car, I think if you stay in an agriturismo like this, then you could arrange in advance for a cooking lesson for your family.

http://www.santuberto.com/index.php

You can read about Campiglia Marittima here:

http://www.abctuscany.com/livorno/campiglia-marittima/index.cfm

http://www.toscanaviva.com/Campiglia_Marittima/Campiglia_Marittima.htm