User blog comment:B214/Volume 23 discussion blog/@comment-31137559-20170307010853/@comment-87.9.173.147-20170308181447

absolutely, it's high probable that he has only 1 children with each girl in that timeline. BUT don't forget that they could be more than 22/24, because when they explained who came back are not only the warriors, but even the ones who were old enough to do it, so it's probable that Issei has other warriors childrens that were not ready to fight a battle back in time, and this would increase even the childrens who were not fighter.