We made a family trip to Rome without a car, and it worked just fine.
We were four (couple, teenager and kid) and had our own bedrooms. Besides, the beds were very comfortable. The kitchen/dining room is ok, but the real comfortable places to stay are the bedrooms.
The location is perfect. We did everything on foot (even coming back from Vatican City, which we went by metro, that is 2 minutes away from the house).
There are two things to pay attention to: the stairs are really tiring (three floors up) and the hot water is short (you run out of it quickly, and has to wait a lot for the boiler to recover).