I agree with the prior suggestions re Florence. Especially if any of you are into Renaissance art / history, Florence (and the Uffizi in particular) should go on your "must-see" list. Generally speaking, the Tuscan countryside is difficult to visit unless you rent a car. Emilia Romagna is easier without a car, though we have always had a rental car in this part of Italy, as well.
In terms of towns in Tuscany, I suggest that you watch some videos, of course including Rick Steves'! Tuscany is a huge geographic area, with many visit-worthy towns. Here are just a couple of them:
We have gone to Siena a number of times; we like a bigger location, to allow for more restaurant choices, wandering around and people-watching. The views from the city over the countryside are hard to beat, and you would have many day-trip options. To stay at, check out Palazzo Ravizza, it was a wonderful and special place to stay, and the views from their back garden area are awesome.
San Gimignano is gorgeous, but much smaller and FULL of tourists during the day. We have stayed here, too, and avoided many day-trippers by taking day trips from San Gimignano, and returning in the evening when it's much quieter. Definitely visit Volterra if you are interested in Etruscan history; they have a good museum.
We liked Lucca, but I preferred Siena, I can't say why, specifically. But Lucca is an interesting city, as well, and the walls around the city area fun to walk or ride bikes on. It kind of depends on what part(s) of Tuscany you decide you want to visit.
All of the Chianti towns are very cute, but if you're not really into wine, maybe you don't need to stay here. You could drive through this area, though, if you stay in Florence, then go into southern Tuscany from there (or vice versa if you visit Florence at the end of your time in Italy).
Emilia Romagna is also great, and we've been here, too, a number of times. The food of Emilia Romagna lives up to anything that you read about it. But I will admit, especially when driving from Emilia Romagna into Tuscany, I catch my breath on entering the hills of Tuscany and its beauty. In Emilia Romagna, I love both Bologna and Modena. Bologna is more of a students' town (in a good way); Modena has less to see in the town, but I love it because it feels to me like a city where real people are living their lives (well, in a more prosperous way). Either are good locations for day trips.
If you rent a car for the four of you, my advice would be to pack as light as possible and rent as small a car as you can - it will make driving on narrow roads and in small towns a little easier than if you had a large vehicle.
