We think the book was part of a series. The first book had a black flocked cover, so it had a soft feel like a velvet fabric. Possibly with a gold castle on the front with stars coming up from it. It was a young adult book, it involved magic.
We think there was a dark green sequel, flocked cover again. Possibly with a silver inlay design this time instead of gold.
Memories of a possible plot include a family, Addams Family vibes, and possibly a squid in a cave at some point....but honestly we read so many that we could be jumbling plots.