Thanks for sharing your story with us. It can be hard supporting a person with a mental health condition when they are living in the same house as us, let alone a person who is some distance away.
I'm making suggestions as they come to mind. Are you able to talk to your brother. Maybe just contact him and have a general chat, then ask how he is getting on and does he need any help.
As a person suffering from depression, I will often lie and tell people I am okay when deep inside I am struggling like crazy. That can be part of depression.
The Beyond Blue website has information on how to assist a person with depression, you may find some suggestions that will work over the distance.
Maybe you could Google to see what facilities/professionals are available where your brother lives. Do you know if he has a regular Dr? Can you ask him to visit the Dr for your own sense of wellbeing?
There can be a fine line between wanting to help a person and having the person push you away. Hope you manage to find the right balance.
If your brother's friend is really concerned, maybe ask if he is prepared to call an ambulance if he feels life is getting too difficult for your brother.
The ambulance people do not have to take your brother to hospital, but it may be a chance to keep him safe if required and start the ball rolling to his receiving help. If necessary the police may be able to assist as well.
I really hope your brother is open to chatting with you openly.
Wishing you all the best from Dools