The Quay is the sensible drop-off for a group, because so much is walkable from it.
In the town
Drop-off serving the Quay and town centre puts Poole Museum, the Old Town, the boat departures and lunch all within a short walk, which removes most of the logistics from a day.
At the beaches
Coach access on the Sandbanks peninsula is constrained, especially in summer. Treat it as a drop-off and pick-up rather than somewhere the coach can sit.
Confirm before you travel
Arrangements, dimensions and charges change. Check with BCP Council and with each attraction before finalising a schedule. See group travel.