Chicago (edit: The Chicago Manual of Style) says that when two nouns “possess” the same entity, only the
second takes an apostrophe (‘):
- my aunt and uncle’s house
- Gilbert and Sullivan’s lolanthe
- Minneapolis and Saint Paul’s transportation system
On the other hand, when two nouns possess different entities, both
possessives take an apostrophe:
- my aunt’s and uncle’s specific talents
- New York’s and Chicago’s transportation systems
- our friends’ and neighbors’ children
In the above source, the following question is raised which remains un-answered;
What about a line in a song I wrote for one of my grandchildren
relating the date he was born to the date my husband and I first met.
The line is as follows:
“………Born upon a fateful date in Mama and Paps’s life.”
or” …..Born upon a fateful date in Mama’s and Papa’s lives.”
or …”Born upon a fateful date in Mama’s and Papa’s life.”
I look forward to knowing the answer to the above question and a general explanation to the rules.
The source you cite provides a good explanation: one apostrophe if the thing possessed is shared between the two entities, two apostrophes if there are multiple things possessed that are not shared.
Either of the first two choices (“Mama and Papa’s life” or “Mama’s and Papa’s lives”) is grammatically correct by those rules.
The first would be appropriate if the author wanted to indicate the shared nature of their married life. The second would be appropriate if the author wanted to distinguish their individual lives from each other–perhaps if they were divorced.