I don’t know if this means more than one ship can use this ability in one turn if a six is rolled. I also don’t know if the same action can be used twice if a six is rolled, like two move or two shoot actions.
If you have different sources of that ability, such as two different crew on different ships, you may make the roll for that ability twice (once per each crew). If you roll a 6, any ship in your fleet may be given two of the four actions, move, shoot, repair or explore. They do not have to be the same two actions, so you could give a ship an explore action then a move action (or vice versa). You can apply the two actions to the ship that the source of the ability is on, in your example, you could give Jean Laffite’s ship two actions, be it two move actions, two shoot actions, two repair actions or some combination thereof.