Possessive forms for multiple nouns When two or more nouns jointly possess one thing, change only the last noun to the possessive case: Mike and Amanda’s new loft apartment is really neat. Please tell Juan and Maria’s parents that they’ll be late getting home from school.

When you have two or more nouns that you're making into a compound possessive, add 's to only the last noun if the nouns are functioning as one unit. Margo and Martha's business was booming. This means that Margo and Martha share ownership of a booming business.

The double possessive, usually using both of and 's to demonstrate possession, is grammatical. While it is sometimes unnecessary, it can be helpful for differentiating when the possessive (or genitive) case is about association or ownership, such as in "a picture of my friend" vs. "a picture of my friend's."