We’ve used a rental car in Italy, including driving to Cinque Terre plus out-of-the-way spots in Tuscany and Umbria last year, as well as around Castagneto Carducci in Tuscany this year. After a week with a car this year, we turned it in and then spent a month seeing more of Tuscan cities and towns by train. The places you mentioned are major enough to be easily reachable by train, but maybe you want a car for flexibility, or for scenery along the way? Maybe (I’m not sure) the car would be cheaper for the 4 of you, compared to train tickets, or not. Some of our train rides required changing trains in stations along the way, to reach the ultimate destination. But have you considered traveling by train after your C.T. time?
In Lucca two months ago, we stayed several nights at Rick’s recommended La Boheme B&B, and it was a pleasant place except for the Friday night we arrived. Fridays seem to be the one night the old town is mobbed with visitors, noisy visitors, and they were still walking the streets and carrying on loud conversations well past 2AM. We slept much better the remaining nights.
Our schedule wound up leaving us just one night in Siena, and we really needed at least one more night and another day … if not even more. If you’ve got just the 2 nights before Rome, I’d stick to the western edge of Tuscany, and see and/or stay in Lucca and perhaps Volterra. Pisa’s not possibly on your list for a short visit en route, right? It was a great stop one day for us,.
Orvieto could make for a very nice day and night, but then where else would you stay? Second night in Orvieto (perhaps), or a too-short Siena the other night? And then you’ve got a longer drive than necessary, just to reach Rome, when a train ride would get that done. Or turn in the car at Orvieto, then do the train? Turning in at the Rome Fiumicino airport requires driving south past Rome, then backtracking to get into the city.