We use the possesive 's to talk about what belongs to people, and sometimes animals, but not things (of may be used here).
That's Sarah's blog.
We add 's to all singular nouns, and to plural nouns that do not end in -s.
My aunt's house is near here. The children's names are Ray and Tom.
We add an apostrophe (') to plural nouns that end in -s:
The students's coffee bar is on the first floor.
Note: Emma and Kate's father is a teacher. (Not Emma's and Kate's father is a teacher.)