User blog comment:B214/Question & Answers 5/@comment-24098614-20150707070424/@comment-100.2.206.203-20150708164508

Usually the male heir becoms the leader, the female gets married into the male clan. For example if Rias married Riser, Rias will belong to the Phoneix clan while Riser still remains in his clan. For the Gremory, the next leader will be Sirzech's child. P.S.: Both gets to keep their peerages regardless.