On Witches:
Satella, Witch of Envy - Satella was not a vassal fit for the Witch Factor, and forcing herself to become a Witch caused her multiple personality disorder. As the evil Witch of Envy she killed and absorbed all the other six witches of Greater Sin and destroyed half the world. The combined effort of Dragon, Sword Saint, and the Sage could not kill her existence, and merely managed to seal her in the Grand Falls.
Her appearance is identical to that of Emilia. Ekidna calls Emilia the Daughter of the Witch.
Ekidna, Witch of Greed - Obsessed with knowledge, she sought to learn more even after death. After her death, her spirit was sealed by the Dragon as a countermeasure to if and when Envy awakens again. Ekidna created a virtual spirit world housed by herself and artificially recreated personalities of the other witches to hang out. She invites Subaru to this lair of witches and gives him advice on his powers. She has since become free to roam the world in a cloned body of her best friend, thanks to Subaru's actions in arc 4.
She is cunning and manipulative, and the mother of Beatrice. She is worshiped by Roswaal as well.
Minerva, Witch of Wrath - Minerva has the power to "punch" people and heal them. Her powerful punches however destroys the world at the same time. Anytime she punches people back to health, catastrophe happens elsewhere in the world. Which causes more people to become injured, and she rushes there to punch them. This infinite cycle of destruction and healing caused more harm than good, but that never stopped her from continuing.