Sorry to be slow getting back to this thread, but life has intervened. Anyway, after some discussion with my library science professor friend, I have the following information:
To deal with multiple authors in a single sort field, where the goal is to make lexicographic sorting 'do the right thing' you have two separate issues:
- Individual names, with titles and epithets and such. A good, non-controversial set of rules for this is http://imagecat1.princeton.edu/ECC/cardhelp.html
- Placing multiple authors or editors or whatever so that the entire combination sorts correctly. For this purpose, place each in the line or field 'most important' first (thus authors ahead of editors). It's considered good form to make the line/field human readable by separating either with 'and' or '&', but this is not strictly required. However, don't use any other separator (assuming an English language catalog). Note, of course, that the presence or absence of a human-readable separator has no impact on sorting as long as you are consistent about it.
I observe that '&' has the lovely feature that it is highly unlikely to be part of any ordinary name (where commas may appear in names like 'John of Gaunt, duke of Lancaster' and periods may appear in names like 'New Jersey. Civil Service Commission.') so it would make a lovely choice for Calibre.