Harry needs to go NC with his family and grieve for the kind of family he never had.
It is clear they are completely dysfunctional. I believe everything he says. He has gained awareness of the abuse going on, but now sees abuse everywhere. It is typical for abuse survivors. Once you have seen it you see it everywhere and it is hard to distinguish which part is the abuse and which part is human.
He needs to spend time with himself, continue to process and come to terms with everything rather than selling it.
In time he might understand that he cannot change them and he cannot convince them to change. They'll either wake up or they won't. He can only decice how he wants to deal with what they give him. He has not yet understood he needs to let go of them, which is the reality of many that have been abused.
William was the golden child and Harry the scapegoat. Trouble is he finds issue with 'normal' things (bigger and smaller bedroom's..) rather than pinpointing the systematic abuse he has suffered.
He's trying to convince the world he was treated unfairly. A sign that he is not ready to let go and wants approval from millions. He is in pain.
Instead of books and interviews, he should write a diary (and not publish it).