It has long been speculated that Joan Marshall was the twin-sister of Writer/Director Dirk Wayne Summers. This may have been started by Joan herself. She always referred to Dirk as her 'brother,' and they introduced each other to their various friends as brother & sister. (They were the exact same age; went to the same elementary school & high-school together, and they did look remarkably alike.) Plus, their relationship was best described as 'familial,' always remaining constantly close. But no definitive information of their being siblings has ever been disclosed; Joan is now deceased and Dirk refuses to discuss the subject.
Mother of son Steven and daughter Shari (from her first marriage).
Was originally cast as the mother character (then known as Phoebe Munster) and was filmed in that role in the test episode of "The Munsters" (1964) shown to network executives. However, she was subsequently replaced by Yvonne De Carlo when filming began for the first season (network executives thought Marshall's Lily Munster was too much like Morticia Addams).
When Joan Marshall married business executive Mel Bartfield in 1990 in Los Angeles, her best friend (perhaps her brother?) writer/director Dirk Wayne Summers performed the wedding ceremony. (Summers became an Ordained Minister in 1969).