Darla and Ellie are siblings. If you think otherwise, take this into consideration. Both Darla and Ellie have red hair, oval ears, messed up teeth, and green eyes. Also Ellie and Darla both have green eyes with Ellie having a mix of green combined with blue matching Darla's uncle the dentist.Plus we never find out Darla or Ellie's parents so how do we know they're not the same?
Theory by Jacob Thor