Can I say, "You can stand in the house Romeo and Juliet fell in love." In this case, relative adverb 'where' was deleted. But I think there should be "in" at the end of the sentence. Am I right? Can anyone answer about this?
Yes, you have to insert either in or where. The reason is that you generally cannot delete where but in certain cases you can delete that/which. Consider the following two sentences:
This is the house which/that Romeo and Juliet fell in love in.
This is the house where Romeo and Juliet fell in love.
You cannot delete where from the second sentence, but you can delete which/that from the first.