Need help writing two new players into current story.

Story is players were shanghaied but the ship wrecked on some seemingly deserted island.

All npc's and player survivors were listed specifically in ships manifest as cargo.

The only other humanoids on the island are part of two groups. One being a group of survivors of a airship/dirigible crash that occurred some time ago and the other being profiteer/slavers who run a large marina (hive of scum and villainy).

The plan was, that the players can join either group depending on how the game went. If players joined the airship survivors they can help them overtake or steal a ship off the island. If they join with the mercs they have them kill off the survivors so that they dont have a group of idealist gorilla fighters causing problems with their less than morally sound businesses, in trade for passage off of the island.

I have two new players joining the group really soon and i have no idea how to write them properly. Now, its obvious that I would just have the new players be members of either group but the current players don't even know they exist on the island yet and won't for some time. Having the other players be from either group would reveal a large chunk of story and give them too much information to work with about where they are and i'd rather have them learn about them by exploring.

Saying there was a third crash to this island seems a bit lazy to me so im trying to consider alternative reasons they would be there without them having knowledge of the groups existence.

The other option is to retcon what the ships manifest said, which makes some other things plot holey, to add the new players who washed up elsewhere.