Add ’s to create the possessive, even for singular names ending in an s, x, z
Jones’s art, Xerox’s bill, Bill Buzz’s restaurant
If the name is plural, add the apostrophe after the s.
the Joneses’ art
With a compound subject, put the apostrophe after the second name:
Doug and Linda’s house
If the subject is not compound but two separate entities, both take an apostrophe:
students’ and faculty’s health plans
Exceptions: Nouns that are the same in both singular and plural form: politics’; species’
Some “for sake” expressions: for goodness’ sake; but for appearance’s sake.