Sorry to hear about your brother. I hope he is as comfortable as can be in his situation.
I don't see anything major happening to his bonds in the short term (next few weeks or months). But the stocks could certainly rise or fall. If you want to be ultraconservative, there is nothing wrong with a 20% stock and 80% bond/cash portfolio. By doing that, you'd have him cash in on the massive stock market gains that happened the last few years and can put it someplace safe. The 20% stocks is just in case his life stretches out longer than doctors think. Living longer than your money is a risk too.
Vanguard mutual funds VUSXX, VMFXX, and VMRXX are all paying ~5.28% interest right now. That probably pays the same if not more than his bonds and is far safer than his stocks. Consider moving a chunk of the stocks and bonds to one of those funds.