Use an apostrophe to indicate possession with nouns. Use the apostrophe with the last name only for joint ownership. Example: Carl and Helen's cat was stuck up the tree.
Instructions: Supply the apostrophes and/or "s" to make the possessives in the following sentences.
1. Smith and Johnson store sells almost everything possible.
2. Jim and Jeff apartment was really dirty.
3. We can borrow Gene and Fred boat for tomorrow.
4. The cat and mouse game ended abruptly.
5. The buyer and salesman discussion brought the buyer a new car.
--For answers scroll down.
Answers:
1. Smith and Johnson's store sells almost everything possible.
2. Jim and Jeff's apartment was really dirty.
3. We can borrow Gene and Fred's boat for tomorrow.
4. The cat and mouse's game ended abruptly.
5. The buyer and salesman's discussion brought the buyer a new car.
from Daily Grammar Lessons Blog
http://dailygrammarlessons.blogspot.com/2018/04/lesson-404-mechanics-punctuation.html