As an adoptee, I am going to do my best to contain my anger at this post and offer you constructive feedback.
This child is 9 years old. NINE. Even if he did whatever he could to get out of an abusive situation, imagine being 9 and having to manipulate the world to survive. To feel safe.
He has experienced multiple traumas and deserves compassion, understanding, therapy, and support. Showering him with gifts is meaningless, he needs to feel safe not spoiled.
One year is a blip in the life of a traumatized human being. It will take him a lifetime to heal and learn how to have healthy attachments.
And honestly, he's been with you for one year and you're surprised he doesn't think of you as his parents?? Somewhere out there he has natural parents, ones that presumably hurt him in multiple ways. Your family is an artificial construct, one that may never feel like family for him. Educate yourselves about adoption, trauma, and attachment issues.
The real problem is NOT that he doesn't see you as parents. The real problem is that he has mental health issues that have nothing to do with you.
His violence must not be tolerated and everyone must be safe. But there is a dynamic at play, one that you contribute to. Your expectations are unreasonable, unhealthy, and unfair. "So we're stuck with a nine year old roommate that doesn't like us" is a devastating sentence. You don't like him, at least own that honestly.