/lit/ - Literature

I was suggested to ask this here:

I'm trying to remember a kid's book I read as a child in the 80s/90s.
(I don't think the book was written during that time.)
It was illustrated, maybe 30 pages long.
It was about three kids playing in their lawn, two boys and a girl, when the youngest boy is kidnapped by a Rumplestiltskin-like character.
He is taken to a castle where kids are forced to stand in the corner, with lots of corners for every kid.
Some mentor (a cat I think) then takes the eldest boy to see various magic people for I think a tear and a seed.
One such person was an underground king where everyone was forced to crawl around.
The girl was tasked with keeping a fire lit, but also to not leave a drawn circle.
The evil dude tricks her at one point and rushes in to stamp out the fire, but she saves it by throwing herself on the fire.
Just then eldest boy returns and quickly goes through magic ritual before sister is burned up.
They win and get their brother back, obviously.
Does this sound familiar to anyone?
I think the pictures were similar in style to Polar Express.

Pic unrelated, just another relatively unknown kid's book I grew up with and loved.