Do pics get multiplied in iPhone's photo app? If we make a album in iPhone's photo app by selecting some photos from 'all photos', would it multiply or duplicate the pictures in the phone? As the pics will be there in 'all pictures' section too and hence would the extra space be occupied the pix of the freshly created album?
No, photos added to albums are references to the original. Deleting the original photo removes the photo from any albums that it has been added to.