Is "Teacher Vera's bike" correct?
Yes!
THERE IS ONLY ONE KID IN THE SENTENCE: Our kid's toys are all over the floor!
Right!
CORRECT OR INCORRECT: That's my parents' house.
CORRECT
CORRECT OR INCORRECT: My grandfather's car is falling apart.
CORRECT
THERE IS ONE MAN AND MORE THAN ONE SANDWICHES: The mans' sandwiches are ready
WRONG!
CORRECT OR INCORRECT: His aunts's loves to ask about "girlfriends".
INCORRECT!
MY MOTHER'S-IN-LAW RING or MY MOTHER-IN-LAW'S RING
MY MOTHER-IN-LAW'S RING
THERE IS ONE SISTER IN THE SENTENCE: Her sisters' bags are here in my house.
Wrong! There are more than one sister