Question: How were the two Spanish galleons placed inside the cave?
Question: How did Jo and her mercenaries know what cove to go to in the Philippines if Drake had just discovered it using the crosses that Chloe had brought with her from the helicopter? If Chloe didn't know about using the crosses and was faked out by the false coordinates then wouldn't we assume the mercenaries hadn't found the location yet either?
Answer: Jo and her mercenaries were at the wrong island, It's when they saw Drake go past them in a speed boat, and not to the island they were on, that's when they realised they had been tricked.