Sure, here are the possessive cases filled in:

1. That is Nam's school.
2. These are Nga's brothers.
3. Those are Phong's friends.
4. There are four people in my teacher's family.
5. How many students are there in your sister's class?
6. Where is your friend's school?
7. This is my parents' bedroom.
8. Mr. Ba's breakfast is small.
9. The engineers' room is on the first floor.
10. These people's houses are in the country.