(Thanks, Spooky. Hope you don't mind me taking some of your lines... :) )
Despite his efforts, Jon could not get his original body; it seemed that in this new reality, there was no such thing as an "original body." You kept what you had in the family until a swap was necessary. He went to sleep that night with his sister's body and his brother's arms, and woke up... changed.
He still had his sister's breasts, but there was a larger pair under them; his mom's. His crotch had two penises side by side and a vagina under them, his dad's, brother's and little sister Sally's, by the looks of them. It seemed, also, that with all these extra bits he was bound to lose something. He had no arms. Jon carefully sat up and stood up on the floor, wobbling and unsure of how he was going to get down the stairs with these jiggling weights on him.
"Want some help, Jon?" His sister Sally's voice spoke from his side, her little head perched on their dad's body, naked but with a smooth crotch. "I wanted to be a Ken doll, so Daddy let me have his body!" She grinned and flexed, though their dad didn't have much to flex. She pulled his head off of his body, exchanging it with hers, and leaving his head on Dad's body. Then she walked downstairs, and switched them again. "Not so fast, Jon! You're stuck with that. I don't wanna be the cow." She giggled and ran off, leaving him in the armless four-breasted body with two cocks and a pussy.
