The family will be visiting Rome, Florence and Venice in mid July.
It's 3 train tickets for 4, with no changes and using only high speed trains. Nothing complicate. Can't you wait for late May and get the tickets for them?A train ticket is just an e-mail after all. I mean as a friend, not for a fee.
Judging from the "sold out tours" I think the all family could watch some youtube videos about how to ride the trains in Italy.
Travel agent or not, they should learn the basic stuff like "look for the train code on the Departures board and not for your destination".
Or "train cars are connected, but walking along the aisles with luggage in tow is a pain. On the platform, Wait close to where your car will hopefully stop".
Or: "You are not taking the train just for the experience, you are taking the high speed trains because any other option would make no sense"