YA book: boy/girl discover alternate world controlled by cube

[Rose]

Helping a friend figure out a book she read in high school (2012ish)...it could have been older book but not older than 80s. About a boy and a girl (siblings?) in a house (maybe theirs, maybe their uncles) and the boy finds an empty chest in an empty room and that’s how he discovers this parallel world that is controlled by a kind of Rubik’s cube made by inventor. The world looks the same but it’s not and that world is descending into chaos or it’s magic is tainted or something. When the cube moves the house does too and the boy and girl get separated when the house moves. The key to going to that world is was moon shining through a red or purple pane of glass. The other world was maybe created by a committee of people.

[Kris]

Rose, can we eliminate The Mysterious Fantasy Cube by Celeste L. Hessler?

[Daisy]

Incarceron or its sequels?

[Becca]

This sounds like The Mansion in the Mist by John Bellairs. The parallel world is accessed via a chest in the attic when the moonlight shines through a specific window pane of purple glass, and the magic cube is called the Logos Cube.