travel time from Fiumicino airport to Rome Termini train station

There is a train Leonardo Express that goes from the airport to Termini that takes 30minutes. But what do you mean "how much time do you need?" I

Leonardo Express takes 32 minutes. Bus or taxi ~ hour

Here is an option you may want to look at-- http://www.fiumicinoexpress.com/?lang=en
bus service directly from FCO to Naples

Would save herding the group through a couple of train stations

You need to plan at least an hour from the airport to Termini just in case you miss the train by two minute and have to wait for the next train. However, it could take a couple hours to clear immigration and customs after you deplane. Could do it in a hour or less if lucky but from a logistic standpoint you need to plan a couple of hours and with a group it is always slower. If it is a group of teenagers add another hour.

Fourteen people is a lot of people to keep track of. Have you considered a private tour company to assist you in hammering out the logistics? I know this doesn’t address your question, but Italy will seem like a chaotic mess after a Trans Atlantic trip. This is especially true in Naples. In any event, have a great trip!

When we fly into Rome, we never book the actual train tickets until we reach Rome. Nothing like United being delayed three hours in Chicago for plane maintenance to screw up a timetable.

I agree with Frank. We flew into FCO last October and it took over an hour to get thu customs. Once you clear customs, there’s about a 5 minute walk to the train (there was some construction going on at the time).