What happens to Noah and Abbey after they escape from Luno and Dusty?

In Chapter Sixteen, when Noah finally makes it back to the dock, Luno is pointing a gun at Noah and Abbey. In response, Noah immediately puts his hands in the air, and then proceeds to jump on top of his sister to protect her. The siblings wait for the gunshot, but it never comes, and then they peek out over the side of the dinghy and see that they've been joined on the dock by the pirate guy, who is there to rescue them and is beating on Luno.

Noah and Abbey then leave in the dinghy, but the engine breaks down when they are only half way home. In addition to the malfunctioning engine, they end up out on the water in a storm. After hours out on the water, Paine and the pirate stranger come out looking for them. When they find the kids and take them aboard their boat, the children learn the identity of the pirate..... it's their grandfather, Bobby.