You just couldn't help yourself. Terra was so hot, and you were overwhelmed with lust for her. On a deeper level, you knew that this was extremely fucked up, but your instincts had taken over. At the same time, you didn't want to face the repercussions of fucking your sister, so you decided to swap families with her boyfriend, Rob. You were careful to make it so only you would notice the change.
Terra was yelling at you as you swapped, shouting "What the fuck did you to my boyfr-brother, babe?" Her voice immediately softened, and you answered her with a kiss.
You two kissed passionately for what felt like minutes, before pulling away. "I'm sorry baby, but I thought it'd be funny. I can change him back, but I kind of like the new you," you said. Her tomboy look was really sexy to your new personality, and you played with her tits through her shirt.
Meanwhile, Terra's boyfriend turned brother scoffed and started walking away, swishing up the stairs. You quickly swapped clothes between him and Terra, so that her current outfit was normal. This time, you allowed her to notice the change. His attire changed into a pink top and denim skirt, and Terra chuckled when she saw him.
"Thanks," she said, "These clothes fit me way better now." You just smiled and went to kiss her again. As Rob walked on the stairs, you felt something missing in your pants, and swapped cocks with him. Your boxers filled out, and you grinned widely. "Fuck yeah..." you muttered, as your massive cock tented your jeans.
What do you and your new girlfriend do next?
(Note: For this branch, I'm aging John up to 16 rather than 12, since most chapters in this story seem to assume he's older anyway).