User blog comment:B214/Question and Answers 4/@comment-66.87.81.210-20150221213108/@comment-25032153-20150222161430

they dont really say but you would think so as after Rias mother had her and her brother the lord would be able to have more kids with the harem with the consent of lady Gremory because she would look at them as sister-wifes much as Rias looks at Issei harem which is part her Peerage mostly the girls as sisters to her.