A group in Rome splits up: somebody wants the Vatican, somebody wants lunch, and by four o'clock you are three separate holidays. A group out of Rome does not, because the day has a shape and everybody is inside it.
The things that work are the ones with a job in them. A cooking lesson gives ten people ten jobs. A tasting gives everybody an opinion. Rafting, quads and the adventure parks are competitive in the way groups like, and the boats have the advantage that nobody can wander off.
Two practical notes. Book earlier than you would for two people — small operators run one group at a time. And decide about the driving before the tasting, not during it: for a group, a driver is usually the cheapest solution per head as well as the sensible one.
Groups also fail in a specific way, which is worth naming: somebody ends up organising, and that person does not get a day out. The fix is to book something with a shape — a lesson, a harvest, a raft, a tasting with a start time — so that once you arrive nobody has to decide anything. Every card on this page is that kind of thing.
Frascati is where most groups actually end up, and with good reason: half an hour from Rome, a dozen estates that take groups by arrangement, and enough of them doing lunch, pizza-making or a walk through the vines that eight people can be given eight different kinds of afternoon in the same place. The Cesanese hills further east are the quieter version of the same idea.
Sizes and minimums are the operator's. Several tastings want four or six before they will open a bottle; several boats have a hard maximum; a kitchen has as many stations as it has. All of that is a phone call rather than a problem, and the number is on the card.