Double, Double, Toil and Trouble (movie, 1993)

The Farmer family is in big debts; they might lose their house soon. The seven year old Farmer twins, Kelly and Lynn, decide not to let this happen. They discover that somebody really mean and shrewd is responsible for all the problems of their family: it's their aunt Agatha! Thanks to the moon stone that she found years ago, aunt Agatha is now a witch. She has supernatural abilities but unfortunately uses them to do bad things. She is malicious and loves injuring others, even her own family. The girls must take the magic stone from Agatha.