Venelana Gremory is the mother of Rias and Sirzechs. She cares a lot for her daughter but maintains a strict demeanor to her due to her position as the next head of the Gremory Clan. She is the one that urged Rias into furthering her relationship with Issei and to manage his harem like she does.
Like her husband, she was also very disappointed at the fact that the engagement between Riser and Rias was broke off. However, she since grown fond of Issei, with Issei having some lecherous thoughts of her because of her youthful appearance and how she bears a striking resemblance to Rias. She teaches Issei how to dance, dine gracefully, and become a proper gentleman so that he does not embarrass Rias at social events in the Underworld. She accepts her daughter's decision to love Issei and has come to like Issei and accepts him into the family. She supports the idea of the harem and tells Issei to always protect the girls and keep them happy.
Venelana was the first member of the Gremory Clan that Akeno met and is the person that taught Akeno all the knowledge she currently has, ranging from how a lady should act to different kinds of knowledge as well as Akeno's studies.
Zeoticus is Venelana's husband and the current head of the Gremory Clan. He, like Venelana, was disappointed that the engagement between Rias and Riser Phenex had been broken off, but currently fully supports the love Rias and Issei show towards each other. While she loves her husband dearly, she also very strict with him for acting silly, such as him dressing as Gomorin. Like Sirzechs, Zeoticus is also very fearful of his own wife Venelana is angered.
Sirzechs is Venelana's oldest child, as well as her only son. He had inherited the Power of Destruction ability from Venelana.
Grayfia is Venelana's daughter-in-law, making her the wife of Venelana's son, Sirzechs. Grayfia is also the mother of her grandson, Millicas. Grayfia is currently a devoted maid for the Gremory Clan.
Millicas is Venelana's first grandchild, his parents being her son Sirzechs and Grayfia. Venelana treasures Millicas dearly, as he does her.
Not much is known of their relationship, but they seem to have a sibling-rivalry as Venelana was born with extraordinary talent for the Power of Destruction, despite not being born in the main branch of the Bael clan. Their relationship is further strained and complicated by the fact they were born to different mothers.
They seem to have a close sisterly relationship. When Venelana learned that Misla and her son were scorned and shunned, Venelana tried to take in the both of them into the Gremory clan, but was prevented by the Bael clan. Like her daughter Rias, she was also deeply saddened when Misla was in a coma.
Not much is known about the relationship with her nephew, but she seems to care dearly for Sairaorg as she tried to take him and his mother Misla into the Gremory clan.