Middle Grade thriller/mystery book from the 2010’s
I don’t have much detail in terms of cover aesthetics or even colours but the general plot of the book is that there’s this young teen girl who is being fostered/taken care of by this couple.
I can’t remember if she previously knows them or not. Anyways she arrives to the house and at first things are normal but then she starts noticing strange occurrences.
We get to read from the POV of a fourth person in the house who watches the teen girl and is upset she’s in the house. We find out there’s a young teen boy that’s in the house, that only she can talk to/see? I think it’s alludes to in the book that he was the couple previous foster child who mysteriously died.
Even though he was upset at the girls presence, he’s not malicious (from what I can remember). I think the big plot twist at the end was that it revealed to him being the couple biological son?