It's definitely not a settled issue. > "Proper Nouns Ending in S" > "AP: Add an apostrophe." > "Charlaine Harris’ books" > "the Joneses’ competition" > "Ch

It's definitely not a settled issue. > "Proper Nouns Ending in S" > "AP: Add an apostrophe." > "Charlaine Harris’ books" > "the Joneses’ competition" > "Chicago: Add apostrophe-s if singular, and add an apostrophe if plural." > "Socrates’s tea" > "the Obamas’ garden" > "Les’s moor" http://apvschicago.com/2011/06/apostrophe-s-vs-apostrophe-forming.html http://apvschicago.com/2011/06/apostrophe-s-vs-apostrophe-fo... > "Nouns, noun phrases, and some pronouns generally form a possessive with the suffix 's (or in some cases just by adding an apostrophe to an existing s)." https://en.wikipedia.org/wiki/English_possessive https://en.wikipedia.org/wiki/English_possessive