that one book that the main character discovers human bones under the house??

[David]

Is it Toni Morrison's Beloved?

[Marie]

Darkest Powers Trilogy by Kelley Armstrong. Not exactly the same but some details are eerily similar.

The main character is a teenage girl who can see ghost and resurrect dead people (necromancer). At one point, she ends up in a house for troubled teens with other teens with abilities. She is locked up in the crawl space under the house by one of them, where she finds old human bones. Also, one of her friends left the house but briefly came back without realising that she had died on the outside. The main character has an entire conversation with her before realising her friend is a ghost.

She was guided to the crawl space by another ghost: a man.

[Eva Clemmensen]

I read a book similar to what you described, but the main character was a boy who discovered human bones in the crawl space under his new house. The bones were of the victims of other little boys killed by a serial killer, and the main character could interact (play) with the ghosts of those boys. The boy gets more and more drawn into this ghost world with the murdered boys - with compelling consequences! Is a very powerful and sad story. It's called 'Lost Boys' and is written by Orson Scott Card.
Could this be the book you are looking for?

[Kris]

Lost Boys by Orson Scott Card - Eva's suggestion

[Lobstergirl, au gratin]

OP's account deleted. Moving to NWNK.