Unexpected Marriage [Completed]

Off and Gun families are so close before then. Their grandfathers were super close when they were young. They treated each other like a brother but they thought 'what if they were a family? What does it feel?'. So one day, both grandfathers promise each other that someday when they have grandchildren they will marry each other for them to become a real, big family. And unfortunately Off and Gun were the only grandchildren of each family.
Are Gun and Off agree with all of this thing?
What are their reaction when they knew all of this?