if you want to see both characters separately just goes to these pages Itsuki Ogano and Natsumi Ogano
In the New Crayon Shin-Chan manga[]
They are first featured in the latest New Crayon Shin-chan Manga volume 11 In the September 2020 issue of Manga Town Page vol 206
In the Crayon Shin-Chan Anime[]
both of them made their appearance in Crayon Shin Chan Special <<Uncle Semashi's Marriage Series>> in their first debut in Episode 1218c I'm going to have a cousin!? [ オラにいとこができる!?だゾ ]