I read half of this fantasy/mystery book years ago and I can’t find it anywhere

so from what I remember it had to have been written in the 2000s or 2010s and it was this brother and sister who were visiting their uncle/grandfather in this old house. and the girl finds a chip in the drywall and picks at it until it revealed a small door. but I didn’t read much of it and I remember the cover was green-washed and had a bunch of small doors and I think the doors led to different places. and there was a rail to the book that had a blue-washed cover. I’ve been trying to look for it but I’m lost. please help!