If spiritual intervention is only your father’s idea, not your brother’s, it’s not likely to help. What your dad can do is pray for his son. What your brother can do is get back into therapy. If you and your mother think that therapists don’t get him, ask your brother if you and your mother can go along for a few sessions to give the therapist your perspectives. That will give the therapist more to go on.
Without meeting your brother personally, I can’t make a diagnosis. It’s possible he has bipolar disorder, OCD, depression, or a psychotic disorder NOS. It’s possible that prior drug use has had more consequences than your brother would like to admit. A qualified clinician needs to see him and do a thorough evaluation. Whatever the diagnosis, it’s clear that your brother is suffering and needs more help than he is getting now. I hope you will be able to convince him to stop trying to sedate himself and instead engage in treatment.
I wish you well,