Compound Possessives :
When you are showing possession with compounded nouns
, the apostrophe's placement depends on whether the nouns are acting separately or together.
Miguel's and Cecilia's new cars are in the parking lot.
This means that each of them has at least one new car and that their ownership is a separate matter.
Miguel and Cecilia's new cars are in the parking lot.
This construction tells us that Miguel and Cecilia share ownership of these cars. The possessive (indicated by 's) belongs to the entire phrase, not just to Cecilia.
Lewis and Clark's expectations were very much the same.
This construction tells us that the two gentlemen held one set of expectations in common.
Lewis's and Clark's expectations were altogether different.
This means that the expectations of the two men were different (rather obvious from what the sentence says, too). We signify separate ownership by writing both of the compounded proper nouns in the possessive form.
When one of the possessors in a compound possessive is a personal pronoun, we have to put both possessors in the possessive form or we end up with something silly: "Bill and my car had to be towed last night."
Bill's and my car had to be towed last night.
Giorgio's and her father was not around much during their childhood.
If this second sentence seems unsatisfactory, you might have to do some rewriting so you end up talking about their
father, instead, or revert to using both names: "Giorgio and Isabel's father wasn't around much . . . ." (and then "Giorgio" will lose the apostrophe +s).
Related Links :
Possessives with Gerunds
Possessives versus Adjectival Labels
Possessives of Plurals
Holidays Showing Possession
Possessives with Appositive Forms