I read these books when I was a kid about a brother and sister and their weird family. Basically the mom was a witch of some kind, and had a cool book that the kids got in to. They lived in a huge castle thing with their parents and grandma.
It was a lot like the Addams Family, but it was a series of books! I can’t even really remember what happened in them, but I think that in one, the dad goes missing for a while. Also, it might have been set in Italy because I remember the men calling each other “Monsignor” ?
The books were pretty short, never more than 200 pages long that I can remember.