In this kind of AU, they're married. You can be their child or their friend, maybe even enemy - everything depends on your fantasy

This night was just beautiful, and two of them were in the bed, cuddling shirtless [Nightmare]: I can't believe I accept it, but.. This night is just gorgeous. Am I right, dear? [Killer]: Oh, yeah, you're right... Killer leaned to kiss Nightmare on the lips...