We will be disembarking in Civitavecchia and would like to take a side trip in private car before returning to Rome. We were thinking stopping at an Etruscan site or some interesting towns then on to Orvieto then to Rome. Is this too much for one day? Any suggestions on where to stop and what to see. Also any lunch suggestions. We will be traveling with people who cannot walk a lot. Thanks K
Google maps shows your general proposed route cover about 150 miles. Factoring in typical two lane roads in the rural areas and the traffic in and near Rome, I suspect you have 5 hours of just sitting in the car. A stop for lunch, some sightseeing etc and my estimate is you are looking at a 8-10 hour day after you get off the boat and actually start moving in the car.
You need to decide if "this is too much"
Italy is mostly hills and any ancient sites will likely to be cobblestone or other rough terrain. Or stairs.
If you have not already done so, I suggest you get a guide book and research the areas you are thinking about and see how suitable it is for your group.