The Editor's Manual
Free learning resource on English grammar, punctuation, usage, and style.
Form the possessive of a plural name by placing an apostrophe after the “s” that makes the plural, as you would for any other plural noun.
“You’re” is the contraction of “you are,” while “your” is the possessive form of “you.” Don’t use “your” to mean “you are.”
“Who’s” is the contraction of “who is” or “who has,” while “whose” is the possessive form of “who.”
Form the possessive of a name ending in “s” by adding either an apostrophe and another “s” or just an apostrophe. The possessive of a plural name takes an apostrophe after the final “s.”