They could take a taxi to road town from anywhere on the island. There are also ferry's from west end.

Whether or not going to STT makes sense really depends on your plans and timing. You have to check out of the BVI, check into the USVI on St. John and then check back into the BVI. You check in to USVI at Cruz Bay on St. John and there is a ferry there to St. Thomas, so that would be the easiest option if you wanted to spend a couple days in St. John. Drop them off when checking in and then you can head off to explore St. John for a couple days.