So in touching the sky, mission where you have to get Auriel's Bow, it's revealed that Vyrthur is a Volkihar vampire. Serana also says something about he was the one who created the "Tyranny of the Sun" prophecy. I guess what im trying to get at is was he being manipulated by Harkon or is it the opposite?

Without telling to much, let me just say it was neither. I could be wrong though.