Really, among the 3 of us, we don't have many options.
However, looking at
Zuhaitz's sheet, I realize he has water breathe. He could cast that on Kwikweg (and maybe Farlh) then the 3 of us can move out underwater for ship sabotage (although that probably needs DM approval). In fact, it might be a better idea to bring more than just the 3 of us.
Xenka actually brought along a 1d6 steel sickle especially for underwater sabotage, but its not going to be very effective. By default, a slashing weapon does -2 damage underwater, but affects wooden hulls for full damage (minus the hull hardness of 6).
So if Xenka casts bull strength on himself to give him a strength sore of 18 (bonus +4) and used the sickle as a 2 hander (1.5x strength bonus), he would be able to hit the hull for 1d6+6 damage. Of which, 2 would be subtracted for underwater combat, and 6 for hardness of wood. So the net damage I would deal to the wooden hull per hit would be 1d6-2 (Ave 1.66 damage per hit).
Given that a hull section has 150 HP, it would take him nearly 10 minutes of non-stop hacking to destroy a section, and thats assuming that the people on board don't notice the muffled banging noise, and the fact water is starting to leak in, and dive into the water to drive off the invaders.