I feel that the word "parent" or even the word "child" should not be used as a magical term that imprisons people with abusers.
Devastatingly sad as it is, this child is because of his various mental illnesses, an abuser. Doesn't mean it's his fault, but ordinary folks cannot cope with it. They don't have the tools, and guilting them with the "parent" label and a lot of assumptions is unfair, imo.
I think we bludgeon people with labels and it is wrong to force this family (in fear for their lives if they take him home) to be destroyed. Likewise, the child needs a safe and sheltering therapeutic home, because that's the only kind that will be humane for him.
On the other hand, when Ronald Regan shut down mental institutions and tossed thousands of mental patients into the street (Rx would cover all that) -- the country's never recovered, homelessness first soared (even before the recession). Some of the institutions were just horrible, but we didn't have community care and enough skilled personnel to replace their function.
I believe if we could create caring and competent institutions for the mentally ill --- small-scale and community based whenever possible -- adults AND children with dire mental illness, who are unsafe to their families or themselves, could be cared for.
That would be one of the social changes a humane, compassion-convicted (and rational) culture would do if money weren't spent on large wrong things.
Hops