User blog comment:B214/Question and Answers 3/@comment-62.178.18.58-20140813224147/@comment-24549585-20140815033959

Its called the Legal Wife. Rias will be the Legal Wife and the other girls will just be his other wives. There is no power struggle the kids of Ise and Rias will be the heirs to the gremory house. And Ise said he would marry Koneko when she got bigger when she asked him to marry her, so there is your proof that Ise will marry the rest of the girls.