Hello I have a trip planned end of June sorrento with 10 people flying in and out of FCO I have some experience on the Italian train system leaving Sorrento we are planning on leaving at around 9 am to catch our 3:25 pm flight out of FCO using just the train system or possibly a car to Naples train then train to Roma termini then transfer to airport
I took the train from Naples to FCO via Termini when getting a mid-morning flight and it worked well for me, but I’d be wary of the train from Sorrento to Naples. It is notoriously unreliable and if you miss your train in Naples you will have to rebook your group on the next train to Rome. Either spend the night in Naples or arrange transport from Sorrento to Naples and hope there are no traffic hold-ups.
Assuming you are asking if your plan could work? Maybe. Maybe not! We had an early morning flight from FCO last year, thank god we decided to book a hotel in Fiumicino the night before. Shuttle bus from Sorrento to Naples took 3 hours instead of a bit more than an hour; our flight from Naples to FCO was cancelled so they put us on a bus - another 3 hours. The only thing that worked as planned was the taxi from FCO to Fiumicino. Trains could be better - or not. Just a cautionary tale...
With 10 tickets at risk, if something goes sideways it is a BIG deal.
Is your party of 10 able to be broken up into 2-3 groups, if bad happens?
In June I would not assume the 'next plane' will have 10 empty seats ( never mind the cost)
If everything works 'per plan' it is ~3.5 hrs from Sorrento to FCO. That leaves only a very slim margin for 'oops'.
With that many people, going to Rome the day before deserves serious consideration.
My $0.02