Which sentence uses possessive personal pronouns correctly?
a.
the squirrel twitched it's tail back and forth.
b.
their's is the one on the right, under the box.
c.
stanley claimed that the papers were his'.
d.
have you seen the cat and its kittens?

The only correct sentence from those you've provided is "their's is the one on the right, under the box" because it's the only sentence using the possesive form correctly.

first sentence -> it's = it is ; its is the possesive

third sentecne -> his' does not exist

fourth sentence -> no possesive form is used at all.

“the first decision that led to brutus’ downfall is when he decided that he would join the conspirators in their plot to kill caesar. the plot did not work. the conspirators had to flee for their very lives. the second decision that led to brutus’ downfall is when he refused to listen to cassius. “ i hope this information you.