Translation:Grandfather and grandmother do not come to our house.
Is the "our" plural? If so, why? Are we honoring the house by treating it as plural?
Notice how in English there is the word "to"? That word is not here in the Hindi sentence, but it is implied. It being there in a way (unsaid!) is what puts the word into oblique case.
"Go to" also takes the oblique.
Thank you Ranzo! You finally gave the perfect explanation I have been searching for!! Take all my lingots!!!!!
Like RanzoG said, there's an implied पर in the sentence - "नाना और नानी हमारे घर (पर) नहीं आते।" But we normally omit using it.
"our grandfather and grandmother do not come to our house" was also marked wrong. I guess I assumed too much.
I used grandad and grandma, but it didn't recognise this is an acceptable translation