If an object belongs to two people (joint possession), we just use one ‘ ’s ‘ and add it to the possessive closest to the noun: Mark is Ann and Tony’s (=their) son. (NOT: Mark is Ann’s and Tony’s son.)

If two people possess the same item, put the apostrophe + s after the second name only. Example: Cesar and Maribel’s home is constructed of redwood. However, if one of the joint owners is written as a pronoun, use the possessive form for both.

It is correct to use two possessive nouns in a row. It is most common to see a double possessive noun used when referring to someone’s family member owning an object. For example, you might use “John’s dad’s car,” where both “John” and “dad” are possessive.