Molly and Rover are never mentioned in the cartoon strip, but were named in a 1991 television special.
It's probably safe to assume that all of Snoopy's siblings (if not his sire and dam) were born (like Snoopy himself) at Daisy Hill, and should therefore qualify as answers to the previous question.
According to Wikipedia, Charles Schulz confessed in an interview in 1987 that he had come to regard the introduction of Snoopy's siblings as a mistake – comparing it to the introduction of Eugene the Jeep (the mysterious animal with magical or supernatural abilities) in the Popeye cartoons: "I think Eugene the Jeep took the life out of Popeye himself, and I'm sure [Elzie] Segar didn't realize that."
© Haydn Thompson 2017