Lucinda, Ruby, and Martha

Lucinda, Ruby and Martha are a group of witches from the novels Fairest of All, The Beast Within and Poor Unfortunate Soul. They are the antagonists of the stories, being responsible for the sufferings and corruption of the titular characters.

Physical Appearance
The characters are described as being "doll-like", having porcelain skin, almost a wooden texture to them, as well as having huge eyes and black hair, wearing paint that covers most of their faces. However, there are variances to each of the three. They are apparently immortal, or at least have an extremely long lifespan, as it was mentioned that their corruption of the Evil Queen occurred "years" before.

Personality
The characters are shown to be extremely manipulative and also extremely sadistic, reveling in twisting people's lives while making sure those they cursed were permanently cursed. This is especially evident with their corruption of the Evil Queen as well as how they tried many times to sabotage Beast's chances of ever undoing the curse. They also have no qualms about manipulating or even harming their own family members, as evidenced by tricking their sister Circe into conducting a fool's errand as well as later putting her into a coma specifically to prevent her from interfering with the Beast's spell. However, they are civil to some degree, as they abhor hostility or even disrespect to themselves or close ones, which led to them cursing those responsible.

Fairest of All: A Tale of the Wicked Queen
The sisters are first seen attending the wedding of their cousin, The First King and his new wife, the Evil Queen, who finds them very strange upon their first meeting.

They introduce the Evil Queen to the practices of alchemy and potion making. They leave her many of their magical possessions, such as spell books, a cauldron, and various ingredients as presents for the Queen.

They also give the Queen an enchanted mirror which contains the spirit of her deceased father. They give an incantation to the Queen for her to recite to the mirror when she wants to summon him. Eventually, The Queen grows annoyed of their random appearances at the castle and forces them to leave. Shocked, they leave in despair, with a newfound dislike for the Queen.

The Beast Within: A Tale of Beauty's Prince
The sisters have a more major role in the sequel, also being given names. Years after their corruption of the Evil Queen, they proceeded to encourage their youngest sister, Circe, into cursing the Prince after he coldly dismissed her for being a commoner. They accompany Circe to the Prince's castle to place the curse on him that will turn him into a beast. During the curse, they spy on the Prince through the Enchanted Mirror, and also send their cat Pflanze to spy on him as well.

Although Circe felt bad about the curse, Lucinda, Ruby and Martha harbored no remorse for the curse and fully intended that the Prince remain cursed, despite it being against Circe's wishes that they not interfere. To this end, when Belle fled the castle, they sent the wolf pack after Belle to kill her, knowing full well she stands a chance to break the curse. Though this ironically ensured Belle and Beast's love for each other grew stronger when the latter saved her from the wolves.

In order to ensure Circe didn't stop them during this instance, they also send Circe on an errand to bargain Ursula for the Beast's former beau's life in exchange for a deal the sisters had made with the sea witch. When Circe returns, the sisters trap Circe in a coma to keep her from causing more trouble. Afterwards, they then have Belle return to her father but she ruins their plans by revealing the Prince's cursed existence to the town. So they manipulate events to have the Beast killed by his former friend, Gaston, and swaying the Beast into releasing him to ensure Gaston knifes Beast in the back before dying. However, Circe awakens and manages to undo the curse just in time when Belle announces her love for the dying Beast, much to her sisters' horror. Circe then threatens her sisters to never ruin Belle and the Prince's life ever again, or she will sell their voices to Ursula, at which they reluctantly comply.

Poor Unfortunate Soul: A Tale of the Sea Witch
The sisters are first seen receiving a visit from Ursula, in her human guise of Vanessa. She requests their help in disposing of her brother King Triton, and in exchange she will help them locate and contact their estranged sister Circe, as well as give them Ariel's soul for a spell.

Throughout the novel, they get more and more worried about their deal with Ursula because of a message that was given to them by Maleficent, that told them to cut all ties with her.

They eventually go to the Morningstar castle, the home of Princess Tulip (the Beast's fiancée prior to Belle), where they learn from Tulip's nanny, a fellow witch, that Ursula has no intention of keeping her end of their bargain because she is keeping Circe as a bartering tool in her garden of souls.

The sisters then display a moment of heroism as they recite various incantations to help Prince Eric defeat Ursula once and for all and kill her. They succeed in doing so and saving Circe in the process, however the magic takes it toll on the Odd Sisters placing them in a deathlike slumber.

Trivia

 * The presence of the Odd Sisters in these books indirectly connects several Disney stories/kingdoms together.
 * It is unclear exactly where they live. While The Beast Within suggests they live in the same kingdom as Belle and Beast, they could very likely live somewhere else and teleport to the kingdom when they place the curse on the Beast.
 * It is revealed in Poor Unfortunate Soul: A Tale of the Sea Witch, that their house is mobile, and is transported to new locations through magic; it's last known location being on a cliffside in Tulip Morningstar's kingdom.