We are a party of 6 in our late 70s and early 80s. Are there taxi vans or Ubers we can call so we’re all together in one vehicle, or should we just hire 2 taxis when we need a drive to some sites?
Some taxis are minivans large enough for 6 people, but most are regular (albeit often large) cars which can accommodate only 4 passengers.
You can use a Noleggio Con Conducente (NCC) service, i.e. a private car service, or limo service) if you book in advance and there are plenty of companies you can search using NOLEGGIO CON CONDUCENTE ROMA. Many offer transfers from/to the airport and also day trips to a variety of out of town destinations and they have vehicles of all sizes.
For regular taxi service you can call or also use the app called ItTaxi, the app of the Italian Radiotaxi association
Uber has entered an agreement with ItTaxi, so you can also use Uber to summon a regular taxi, instead of ItTaxi. Just be aware that Uber adds a commission fee of about 3 euro per ride.
Another app you can use is FREE NOW. They also apply a commission fee.
to visit the city of Rome, most locations are easily reachable on foot or using buses or metros or light rail tramway. Obviously if your older members of the party have mobility issues, then there might be limits to the amount of walking they can do.