Victorian-style setting fantasy book involving an ancient and sentient(?) moor/forest. SOMEONE MUST KNOW! :'(

Please help me try to find this book! It has been incessantly resurfacing in my mind for at least ten years!

I can't remember anything important - anything to do with title, author, character names. I'm hoping for a miracle.

These are the things that I think I remember:

The setting is a fantasy Victorian England kind of vibe. The main character is a young female and may be blonde. She has some kind of unknown connection to the local wild woods/moor land that people aren't supposed to go near. The wild woods/forest are somehow supernatural. They have some kind of intent of agency. I think the main character is connected to them through family or heritage. Despite the woods being dangerous, she ends up going pretty close to them because she moves into a manor-like house, either to take care of it or to marry the mysterious man who lives there. There may also be a room or attic in that house that has strange and wonderful invention-type things in it, that I think are connected to her father. And for some reason I feel like they had to do with bending light or had glass globes or something similar.

Other characters I remember are a brother and sister who are a bit down on their luck. They either live in temporary accommodation or are staying at some kind of inn. I think the sister starts working there as well, as a seamstress or something similar. There is also a young man who seems to be a suitor for or is pursuing the sister. He's shady though, I remember expecting him to be revealed to be bad/evil/got creepy vibes. The brother and sister are either twins or look very much alike, to the point where the brother can actually disguise himself as his sister. I don't remember if he had some kind of magic or ability that let him do this, but the disguise was so good that he used it to become his sister around the creepy suitor. The brother (as sister) and creepy suitor are in a carriage at some point, and I remember getting the creepy vibes then - maybe the brother is almost found out in that moment?

I don't think it was a Young Adult Fiction book - I think it was Adult Fiction. It may have also been part of a series, probably the first book, though I don't know if the rest of the series was complete then or if maybe I think it was part of a series because I didn't finish the book. I don't remember the ending.

Also, somehow something green, whether cover or something else I don't know.

If anyone can solve this puzzle for me and find this book, I will be eternally grateful!!