Kyo's Mama, Shinotaru, has basically just done Hatsune Miku mobage game art
Scarle's Mama, RIZ3, seems to have mostly stuck with doing promotional art for Nijisanji
Ren's Mama, Aco Arisaka, did the character designs for Kado: The Right Answer, and is the artist for Makoto Sanada's manga Bestia.
Maria's Mama, Ji mag, has done some promotional artwork for Arknights
Aster's Mama, Amaichi Esora, has done some manga, like a FFXIV manga, and the art for an LN.
Aia's Mama, Noy, has worked on character art for Fire Emblem Heroes, and a promopiece or two for Arknights.
None of them have much to their name, really. The common denominator is that most if not all of them have been hired in the past to illustrate merchandise for Nijisanji.