Well, I can tell you the real life nicknames of the actors as I recall having read them in various books and articles.
Jonathan Frid is known as Jon. John Karlen is Johnny. Kathryn Leigh Scott is Katie. Alexandra Moltke is Alex. Louis Edmonds was known to some as Lou or Louie. Dan Curtis is (predictably) DC or Dan.
I can't think of any others at the moment. Grayson Hall did not really have a nickname, but some of her fans used to call her "The Big GH."
Gothick