What to Know
Names are proper nouns, which become plurals the same way that other nouns do: add the letter -s for most names (“the Johnsons,” “the Websters”) or add -es if the name ends in s or z (“the Joneses,” “the Martinezes”). To show possession using an apostrophe, add ’s for individuals (“Smith’s car”) and just the apostrophe after the s for plurals (“the Smiths’ car,” “the Martinezes’ dog”). By convention, names from classical mythology and the Bible ending in s show possession with the apostrophe only (“Jesus’ teachings”).
The plurals of last names are just like the plurals of most nouns. They typically get formed by adding -s. Except, that is, if the name already ends in s or z. Then the plural is formed by adding -es.
the Smith clan → the Smiths
Jill and Sam Clarence → the Clarences
Mr. and Mrs. Jones → the Joneses
the Fernandez family → the Fernandezes
Unlike regular nouns that end in y, names that end in y are also made plural by adding -s:
the Kennedy clan → the Kennedys
the Daley family → the Daleys
Possession And Names
If you want to talk about something that belongs to more than one member of a family, you start with the plural form and add an apostrophe to show possession:
the Smiths' car
a party at the Fernandezes' house
the Daleys' driveway
If you want to talk about something that belongs to a single person being identified by last name, you follow the usual -'s rule for most names:
the car that belongs to Smith → Smith's car
For names that end in an s or z sound, though, you can either add -'s or just an apostrophe. Going with -'s is the more common choice:
the car that belongs to Jones → Jones's car or Jones' car
Special Rules for Classical Names
For classical and biblical names there are other rules. For names ending in s or es and having two or more syllables, you usually just add an apostrophe. If the name is only one syllable, add -'s.
The names Jesus and Moses are always made possessive with the apostrophe alone:
Silent Ending Letters
The usual way to show possession with a name that ends in a silent s, z, or x is with -'s.
Didier Deschamps's career
Josquin des Prez's music
Eugène Delacroix's paintings