I first saw "Campbell" being used for Serena and "Butler" for Melvin on IMDB in the late 90s. Either name was ever used for any official sources that I could find. Molly was given the name "Baker" in the episode "Who is that Masked Man?", but the Mixx novels use "Baker", but called her "Molly Brown" in volume 2. Melvin appears to be named "Melvin Grier" in the same Mixx novels, but never got a family name mentioned in any episode. Mrs. Baker (Molly's mom) having the first name "Susan" was another of those IMDB things I believe.