Salt by Hannah Moskowitz

Their parents went off to kill a monster and never returned.  The children left behind assume the monster won that battle.  But the eldest wants to go see what happened. She runs the ship, so off they go.

Chronicle Books and Edelweiss shared this book with me for a review (thank you).  It will be published October 30th.

They are killing monsters on the way, so it's not a direct trip.  Her brother meets a pretty lady, sleeps with her, and then finds out she's a pirate.  When they back to their boat she's taken all their weapons and the sail!

Their way is rough and being a monster killer isn't easy, but they do the job.  They even get ripped off by the same pirate again.  Life isn't easy as a monster hunter...