They will overload the ferry boats. I have seen people with advanced paid reservations refused boarding due to overcrowding . If you are planning on leaving tortola the same time as them, Either get to the ferry very early or plan on a water taxi.

Warren S/V Scuba Doo
Lagoon 50 (winner of best crewed yacht under 55 feet at the St. Thomas crewed yacht boat show).

https://www.cyabrochure.com/ebn/2307/pdyrX/6642/4///