The SInister SIsters are the trio of young evil witches attending Witch University in Halloweentown and the daughters of Silas Sinister. They are minor villains in Return to Halloweentown. While Sapphire Sinister and Sage Sinister act as the twin-followers, their sister, Scarlett Sinister acts as the ring-leader.
Scarlett Sinister is portrayed by Kristy Wu while Sapphire and Sage Sinister are played by twin sisters Katie Cockrell and Kellie Cockrell.
The SInister Sisters
They secretly defy the "No Magic" rule of the Witch University by using their powers whenever there is no teacher watching.
They work with a few professors and their father who are the members of the Dominion, to make Marnie open a box with the Cromwell family's ultimate magic in it.
In the end, their plan backfires and they lose their family magic as punishment for their father's actions and that of his co-conspirators.