The wt Jenny mentioned is by MaGtRo.
Get both Sam and Hannah on the floating island. Go back to Bosch tunnel.
Get Sam to go to Bosch tunnel.
Leave Hannah on the floating ship and to go back to Matia Island all by her lil ole self.
Sam should have a new CD taken from the ghost monk inside the temple(inside the room with a small altar) when he gave the oil to him.
Get Sam to walk outside the temple back to the fish balloon.
Fly to the island with the air compressor puzzle.
Calculate the new coordinates from the CD.
This new coordinates is the one for Matia Island.
Fly to Matia Island and be on the other side of the grilled gate.
Get the key you wanted and open the door and have a reunion with Hannah who should be on the bottom floor here.