1. I've got a friend who he plays professional basketball. (he)

2. You should try and relax yourself before you go into the interview. (yourself)

3. That's the house where I lived as a child. (correct)

4. The houses in our area they have been damaged by flooding. (they)

5. Have you behaved yourself today Sarah? (correct)

6. I'm so nervous. I have my own driving test this afternoon. (own)

7. He's probably the best teacher whom I have ever had. (whom)

8. Anybody who found misbehaving will be asked to leave. (who)