Your brother is very lucky to have such a caring sibling. I’m sure it’s very difficult to have him back in the house and causing so much turmoil. Unfortunately, he is more interested in blaming people for how things are than in doing what he needs to do to make his life better. He covers profound discouragement about his life with excuses and defensiveness. Unfortunately, no one can make him take care of himself. Therapy really would help. (If it didn’t, how could there be so many therapists in the world?)
Since he won’t go, I strongly suggest that the rest of you do so. A therapist can help you and your folks figure out how to handle your brother and perhaps get him into some treatment. Do invite your brother to go along to the appointments. Tell him you are all going to spend the hour talking about him. Knowing that, it’s usually difficult for a person to stay home. Often they want to go along just to set the therapist straight that it’s all everyone else’s fault. A skilled therapist will find a way to engage him.
I wish you well.