Kraven didn't kill Lucian. They had a deal where Lucian would cut off some of his skin and Kraven could become the leader of the Vampires and pretend that Lucian was dead. The feud started when Lucian fell in love with Viktor's daughter, got her pregnant, and Viktor killed his daughter to prevent the hybrid from being born right in front of Lucian. With Selene and Lucian's blood, Michael becomes the hybrid. The Lycan killed the Elder Amelia. Selene kills the Elder Viktor. Kraven kills Lucian. As the movie ends, the blood of the imprisoned Lycan flows and awakens the last remaing Vampire Elder. An Selene fears that instead of being the hunter she'll become the hunted. Then it cuts to a scene of the vampire elder descended from Corvinus. The blood of the werewolf Viktor killed in that room drips into his mouth and his eyes narrow like Michael's eyes did, leaving the possibility of a sequel.