Wait

Jack look at his father and feels his cum still dripping from his cunt.

"I wanna see him change." He says, looking forward to get his ****.

Kate smirks and rubs her brothers... currently more like her twins, breasts.

"Hey, stop that Kate."

"Shhhh... don't wake him up."

Jack does not. And after getting fucked by his own dad, what's a bit of fondling between siblings?

He starts making out with his sister and a devious plan forms in his head. He rubs his own pussy, slick with thick baby batter, and coats his fingers with it.

"Hmm you like kissing girls Kate?" He asks his sister.

She laughs and squeezes his butt. Jack take the chance and slips his cum-covered fingers in her pussy, giving her her share of their dad's virile swimmers.

Kate lies down next to her sleeping father and her 'brother' continues fingering her, getting more and more cum in her.
"Oh yes Jackie, that feels good!"

And then they see their dad starting to transform...

His strong jaw softens and turns female, his whole body shrinks a few inches, he is may be even smaller than his children. Breasts start to grow on his now hairless chest. They are much bigger than Jacks or Kates, probably around an E-cup with hard protruding nipples. His abs disappear and his waist clinches together, but his hips flare outwards, giving his body female curves. And his cock... his cock shrinks and shrinks, until it disappears into a vagina.

Jack feels Kate's pussy tighten around his fingers, as she cums at their dad's transformation, he can nearly feel her tight channel sucking all of their fathers cum into her. Kate doesn't realize that Jack may have knocked her up with, instead she grins as she looks at their father.

"He is still sleeping! Oh god, that' priceless." Then she smiles and giggles. "Oh wait, I have an idea! Spread your legs!"

"What? He..." Jack frowns, but Kate simply pulls his legs apart.

"Let him have some of his own... medicine."

She fingers Jacks pussy, which is still rich with cum, until she get's a big load on her hand.

Which she starts to push inside their dad's new and probably very fertile vagina.