Possessive nouns are used to indicate ownership.They are formed by adding an apostrophe (') and s.
(cat's food, dog's house)
When a noun is plural and ends in s, just add an apostrophe (').
(parents' house, friends' party, cats' medicine)
If two people own one thing, add the apostrophe and s to the second person only.
(Tom and Jane's house, Carl and Tom's car)
If two people own separate things, add the apostrophe and s for each person.
(Tom's and Jane's house, Carl's and Tom's car)