SOLVED. MG Book About Monsters [s]

[Annie]

I'm helping my brother find a book. Here's what he remembers:
It was about monsters (many kinds), possibly with "monster" in the name. Two kids had to rescue their dad, probably from evil monsters. They find a secret room in their house, and discover that their dad is a scientist. He's pretty sure that the father was at one point in some sort of lava cage. The book included an appendix with color pictures and facts about the monsters. He thinks the cover was green and pretty simple, but he's not 100% sure.

He read it around six years ago (when he was around 8-9). Thanks!

[Tab]

The Monstrous Memoirs of a Mighty McFearless sounds like it.

With the help of Dr. Devilstone and a book called the Monstranomicon, Minerva and her brother Max go to the evil Zarmaglorg's Castle Doominstinkinfart to rescue their father, whom they have discovered comes from a long line of monsterminators.

[Annie]

Yeah, that's it! Thanks.