Find the nearest public hospital with Jabatan Psikiatri

Make an appointment with the psychiatric department to discuss application of admission of potentially INVOLUNTARY patient (please, please, PLEASE get all relevant documentation [medical reports, psychiatric reports, IC copy, whatever] in order)

Look under Section 10 route:

Mental Health Act 2001 – Safeguarding the Welfare of the Mentally Disordered

Does a Malaysian with mental illness NEED to be put in a mental hospital?

Ooooo. Repeat case ini macam.

You'll have to make another appointment with the hosp department that took him in to discuss the situation (especially with the threat of physical destruction/violence). No need to bring your brother yet.