Actually, the final two bosses come to find you...so when the fight started, I just ran to the river and waited. (There is a water access part visible from the castle front steps...has a half wall on one side, and a covered walkway on the other side).
Once one guy went into the drink, (and the next cutscene played), I just hung out by the river and watched the castle steps for Boss #2's arrival. He showed up, and I lured him toward the water (that half-wall works great for that). I used an air-throw ("Rain" combo), and pile-drivered him into the water. The End.