The 8 player requirement to gain access to the last journal could be swapped with a 2+ any size crew in an alliance requirement.
The two crews in an alliance could be two solo sloops or two galleons it does not matter.
As far as what happens to the other spots around the object that aren’t filled by actual players in the case of two smaller crews attempting to access the final journal…
Friendly Phantom Pirates such as those found in the Athena’s Fortune Hideout could spawn in the empty spots and begin to join the actual players in the ceremony.
Point is, access to the final journal could be more accessible. Rather than requiring 8 players to access it, why not make it 2+ crews of any size in an alliance?
