I got it wrong by using home instead of house. I thought घर is home and मकान is house.
I believe what you are speaking about is when it is in oblique case, which is when a post position applies to it.
The following link may help you to better understand oblique case: http://www.learning-hindi.com/post/1116750602/lesson-48-nouns-in-the-oblique-case
I have what might be a dumb question...why is the noun phrase उनका घर not in the oblique case due to में ? Thank you.
I don't understand why 'uska' is translated as 'their' and not 'his' or 'her'. Shoudln't it be 'unka' if it's translated 'their'?