The Halloweentown movies’ focus on the Cromwell and Piper family leaves some major mysteries about key members, including what happened to Marnie, Dylan, and Sophie’s father. Disney’s 1998 movie Halloweentown reveals that 13-year-old Marnie Piper (Kimberly J. Brown) and her siblings Dylan and Sophie are being raised by their single mother Gwen Piper, who is visited by her eccentric mother Aggie Cromwell every Halloween. The three kids soon find out that they, alongside their mother and grandmother, are witches and a warlock, though their father was a mortal human, explaining why they don’t reside in the magical Halloweentown.
https://screenrant.com/what-happened-marnie-father-william-piper-halloweentown/