Other mistake: When Max and Dani go into Allison's house, and she goes to get cider, when she comes back she says "by the way Dani, I love your costume." But Max doesn't introduce her other than "my sister" so how did Allison know her name?
Other mistake: After the Sanderson sisters are done sucking the life out of Emily Binx, they do a little dance thing after they become younger. When either Winifred or Mary swings past her, Emily's leg moves even though she's supposed to be dead.
Factual error: When the witches follow Mary into the alley after singing I Put A Spell On You, Mary Sanderson said she smelled Scrod, a bottom feeder that would be good with margarine. 300 years prior to that, butter would be the topping of choice as margarine hadn't been invented until the 1800s, when the sisters were dead.