I believe it is instanced, like some of the Pirate's Life Tall Tales, so only one crew can exist in an instance at a time.
Please anyone correct me if I'm wrong.
RealStyli
Vanguard
Insider
Other crews will not be able to go to Mêlée Island with you, although the very start of the Tall Tale involves voting to start it at an outpost and sailing to a portal. This part is in the shared world. Once you get to portal, the rest is just you and your crew.
