In my opinion, the only sentence that is punctuated correctly is #1, regardless of the number of brothers he does or doesn't have.
The distinction I drew out in post #2 is explained in the US Government Printing Office Style Manual (2008) HERE
8.41. To set off words or phrases in apposition or in contrast.
Jean's sister, Joyce, was the eldest. (Jean had one sister.)
but Jonathan's brother Moses Taylor was appointed. (Jonathan had more than one brother.)
The quoted text is correct as it is, unless you make the assumption that the writer is thinking only of Jean and Joyce.Panj?
Jean's sister, Joyce, was the eld
ester. (Jean had one sister.)
The link I included above has expired. It was the result of a search for comma from the home page: http://www.gpoaccess.gov/stylemanual/PS. When I followed your link absolutuley nothing happened, uh?!