Seek medical attention immediately.

You should support and encourage him to meet with a mental health professional for an initial evaluation If possible, you should accompany him to explain your observations and concerns. He will likely benefit from a combination of psychotropic medication typically prescribed by a psychiatrist and psychotherapy where he will generally meet with a psychologist. If he is a danger to himself or others, you can get immediate help by encouraging him to admit himself to an inpatient treatment facility. As a last resort, if he is a danger to himself or others, you can contact the police who will escort him to a mental health facility to keep him safe and to start treatment. It is generally a better experience for the patent when he voluntarily seeks treatment and helps choose the place where treatment occurs. As for yourself, you should make a point to exhibit good self-care and potentially meet with a mental health provider for support and guidance with your specific circumstances.

Seek out therapy for him ASAP.

The first thing you should do is put it in the hand of a professional behavior. Second help you accept your depression.
Be on your side supporting it.
Respect your silence.
Do not precede it, transmit hope, reinforce it positively.

Reading between the lines, I think I am hearing that your brother’s behavior is feeling scary. Perhaps he is threatening verbally or physically towards you and/or himself or others? If so, you must get him to an eval or have the police or a medical person do so. Medication may be necessary to reverse such symptoms.
Please don’t hesitate to do what is necessary. He would thank you later when he is back to normal.

Peace,

Marian Shapiro

You can try to talk to him, but it seems that he needs to talk to a therapist for a few sessions at least and you might need to talk to one, if you feel the need too. We all need to take care of ourselves, before we take care of others.