User blog comment:B214/Volume 22 spoilers/@comment-213.120.234.106-20160720102919/@comment-1359322-20160721040746

If that were the case, then Sirzechs and Rias wouldn't have such a huge gap in age, Millicas and Rias wouldn't have such a small gap. Zeoticus and Riser's father wouldn't have made the wedding engagement between their children. Remember the Phenex siblings are considered rare already due to having 4 siblings. We can argue about Ise having 20+ children, but remember not all of his wives are Devils or Reincarnated Devils.