You are correct about the stress over your family situation weakening your brother's immune system.
Shingles is caused by a reactivation of the same virus that causes chicken pox, which is herpes-zoster virus. After the initial bout of chicken pox, the virus takes up residence in dorsal root ganglia...these are bundles of nerve cell bodies alongside the vertebrae, they are the bodies of the sensory neurons that run into the spinal cord.
The zoster virus tends to reactivate in times of weakened immunity...due to other illness, immunosuppression, and yes, stress as well.
The blisters will occur only on the area of the body that is innervated by the affected nerve. Also, remember that the virus is living in a sensory nerve. That means that your brother may have exceptionally high sensitivity to touch, et cetera in that area.
The anti-viral you are mentioning is likely acyclovir, which is the first-line treatment for this virus. Acyclovir has a pretty good side-effect profile, which means it shouldn't cause your brother many problems. Aside from that, I'd recommend lots of rest.
So I didn't want to worry you too much by mentioning the possibility of permanent neuropathy (the hypersensitivity I mentioned in my #15), but others mentioned it. It's only a small minority of shingles patients that develop this, so don't get too afraid now.
The vaccine that some folks were mentioning is actually the chicken pox vaccine that is given to children. Some studies have been examining if administering the vaccine to adults over 50 years old helps to prevent shingles, as the chance of an adult developing shingles at some point in life (especially in old age) is pretty significant. I don't think that there have been any conclusive results on the studies yet.
Phantom pretty much told you what you need to know. Anti-viral's are probably going to be of limited help. If taken early on, they may lessen symptoms (since they prevent more virus from replicating), but usually don't do much.
Some people get "post-herpetic neuralgia", which is a fancy name for nerve pain after shingles. The treatment is usually Neurontin, or (I think) some of the tricyclic antidepressants (Tofranil, Trazadone, etc).
The drainage from the shingles is contagious until they are crusted over. I would imagine that he will soon be developing the rash soon. No need to avoid other people, as long as it is covered. The only exception: people with compromised immune systems should steer clear for a while.