User blog comment:B214/Question and Answers 6/@comment-25072311-20190401190525/@comment-155.93.250.79-20190424072618

Well according to the devil page, it is quite hard for pure blooded devils to give birth, and the Phenex family is a rare case with 4 kids. Also this applies to Ravel as well, this is also the reason why Rias and Ravel's children with Issei were down in the middle rather than among the first born.

Here are Issei's children according to age and their mother

Akeno Himejima (currently engaged/Volume 22) - Kurenai

Asia Hyodou (currently engaged/Volume 23) - Airi

Xenovia Quarta (currently engaged/Volume 23) - Zen

Irinia Shido (currently engaged/Volume 23)- Shin (Interesting considering the new light novels)

Rossweisse (currently engaged/Volume 25)- Helmwige

Rias Gremory (currently engaged/Volume 22)- Ex

Ravel Hyodou - Robertina (Born the same year as Ex)

Elmenhilde Karnestrin - Ernestine

Koneko Toujou (currently engaged/Volume 24)- Shirayuki

Kuroka (currently engaged/Volume 24)- Kurobara

Le Fay - Mordred - Age Unknown

There are more but they weren't old enough to fight.

check links

https://highschooldxd.fandom.com/wiki/Devil

https://highschooldxd.fandom.com/wiki/High_School_DxD_EX