SOLVED. Book about humans touring hell/underworld [s]

[Akiad]

This book was aimed for a young adult audience. It was centered around a family, the father of which was the (keeper?) of hell. It was their duty to maintain the underworld so that humans could tour it for entertainment. After many failed examinations of the underworld by humans, they seek to shut it down. I think the book title or main character name was similar to or resembled Darkly, I'm not sure though.

[Kokomomomo]

The Dark Lord of Derkholm? Not the underworld, but the father is the current Dark Lord.

[Akiad]

That's it! Thank you! Sorry I may have confused some or the details of the book.