The Hades family consists, the eldest brother Acheron Hades, Lethe Hades, Styx Hades, Cocytus Hades, Phlegethon Hades and the only sister, Aornis Hades. They are from the Nextian Universe, and most of them are evil, with the exception of Lethe, who is the white sheep of the family.
At one point, Aornis had a daughter called Jenny, on whom she based the mindworm Jenny Next, but she died and never appeared in the books.
Little is known about their parents, but their mother was still alive as of Lost in a Good Book, as Aornis said she was annoyed about Acheron's death.
Many, if not all of them seem to have strange powers. Aornis is a mnenomorph, meaning she can alter people's memories, and she also has control over entropy. Acheron can control weak-willed people and does not show up on cameras. He is also invulnerable to everything except silver.
Thursday Next has come up against and beaten Acheron, in The Eyre Affair, Aornis, in Lost in a Good Book, The Well of Lost Plots and The Woman Who Died a Lot. It was said in First Among Sequels that she had also met Cocytus, possibly in The Great Samuel Pepys Fiasco, and in The Woman Who Died a Lot, Aornis said that Thursday had killed him.