The Encyclopedia of Walt Disney's Animated Characters: From Mickey Mouse to Hercules by
John Grant

Walt Disney Character Description of Anastasia Tremaine and Drizella Tremaine from "Cinderella" (1950)

Anastasia Tremaine and Drizella Tremaine are the epitome of spoilt chrildren - the worst type of spoilt chrildren, in fact: those who stay that way right through into adulthood. Their voices are raucous and grating; their singing is dire; their faces are milk-curdling; their dancing is a little short of terrifying... but all of these things might be forgiven them, and they might succeed in finding their own Prince Charmings, were it not for the fact that their innate selfishness shines through in their every word and deed. In fact, they could be as beautiful as Cinderella and yet still be repellent for exactly this reason: a marvellous part of the Disney characterization of them is that they are not physically too revoltingly ugly.
In terms of personality there is little to choose between them (Drizella is the one with the dark hair), but this in no way diminishes the cleverness of their characterization. Moreover, they provide a welcome burst of slapstick humour among the movie's baddies, because they are in truth such buffoons. That said, they are not the kind of stepsisters that you or I might wish to have: comedians or not, they make poor Cinder's life a daily hell.