Sometimes, it seems like you double up in indicating who or what is owned by something else. Compare these two sentences:
The first sentence is talking about the memories that his grandfather has of something, which the grandfather is probably telling the boy about. The memories are owned by the grandfather.
The boy was scared by the memories of his grandfather’s.
The boy was scared by the memories of his grandfather.
In the second sentence, the memories are not owned by the grandfather. They are someone else’s memories of the grandfather. Perhaps the boy is being told some scary things about what other people remember about his grandfather.
The first sentence is an example of a double possessive construction. It has two ownership parts stacked on top of each other. The ‘of’ part indicates one ownership, and "grandfather’s" indicates another ownership - there’s double possession.
In the second sentence, the phrase ‘of his grandfather’ is an adjectival phrase that tells us more information about the noun ‘memories’.
Mixing up it’s and its
It’s and its have two different meanings.
It’sUsually when you have an apostrophe followed by an ‘s’, it means that the word is a possessive word and it owns something. Not so with this word, however. When you see it’s, it is actually a shortening of the words ‘it is’:
‘Its’, on the other hand, is the possessive form of the word ‘it’. ‘Its’ is a possessive pronoun. So use this form when you’re talking about what ‘it’ owns:
I am surprised at its size.
Hope it's helped you!