Your brother most probably having a psychotic illness. he need to get examined by a psychiatrist
, to have an accurate diagnosis.
The practical problem here is not diagnosis of the condition, but getting him into regular treatment. If he is not willing to take treatment, he can be admitted to a hospital under appropriate section. This can be done in many countries if he is potentially dangerous to self or others.
Easier is to treat him next time he gets into jail. You as his sister can approach court and appeal that he is mentally ill and needs treatment. Court will get him examined by a psychiatrist and order treatment. By the time he is out he will be better and it will be easier to continue treatment. He may need follow up treatment for long periods.