You are in a difficult situation. Contact with other people along with exercise is important to work one's way out of depression. Most likely, this is remedy will be opposed.
Have you considered a home care agency? Do you think that having a certified person in the home on a regular or semi-regular basis might be good for your brother? Insurance usually requires that the person needing care has self help issues in order to qualify for this service, but it sounds as if your brother could afford this help.
There are assisted living facilities, and I have seen some very nice ones for well educated people. Individuals have their own apartments, but also have opportunities to mingle with other people for exercise classes, lectures, dinners, outings, music, plays, etc.
A social worker might have good suggestions about what is available in your community.
Also, so that you don't have to worry, can you encourage him to carry a cell phone, so that he can call in an emergency.
I don't know the extent of your brother's depression. In the worst stages, it can be deadly. An evaluation is approprite, even though it might be difficult to convince him of this.
Technology may be available. I'm sure there are books on the subject of depression, perhaps ones that he can read himself, so he gets involved in planning for his own recovery.
I wish you the best,