Are there friends or other relatives with whom your brother regularly interacts? If so try to gather more information from them. They might know the name of his doctor and other important information.
Your family might consider intervening as a group. Another idea to consider, if your brother would be willing, is family therapy.
In the meantime, monitor his behavior to ensure that he’s not in danger. This won’t be easy but do the best you can. If you suspect that he may be in danger, contact your local mental health crisis team. They can come to the home and assess his mental health. If they decide that he needs inpatient hospitalization, they can make the proper arrangements.
Consider contacting your local National Alliance on Mental Illness (NAMI) support group. NAMI is an advocacy organization with active support groups in many communities throughout the United States. Their support groups are staffed by people who are veterans of the mental health system. They can direct you to specific resources in your community.
It can be difficult to help someone who is paranoid and who is actively attempting to keep others out. Your options are limited but hopefully the aforementioned ideas will be helpful. Please take care.
Dr. Kristina Randle