Complex sentence: Casper accidentally lets it slip to the Ghostly Trio that Wendy and her aunts are witches, when they are attacked by Desmonds two thug warlock enforcers.
Split into simpler sentences: Casper accidentally lets it slip to the Ghostly Trio that Wendy and they attack Wendy and her aunts. The witchs are attacked by Desmonds two thug warlock enforcers.