Jenny had an idea, why not involving more people into her fun time? She decided to call her best friend Eva and her other friend Tyson, both of them were friends of Jeff too.
Jenny quickly grabbed one of Kat's shirts and wore it, just leaving her horse part naked. After some minutes she greeted both of her friends and entered, acting like it was completely normal to see their friend as a hermaphrodite centauress.
"By the way, have you seen Jeff and Kat? I haven't heard about them" Tyson asked as they went up the stairs walking to Jeff's room.
"Yeah, me neither" Eva added combing her curly red hair.
"All answer everything, but for that I'll need to show you something really good"
As they reached the room Jenny explained everything to them, from the magic computer to the transformation of the siblings that resulted into parts of Jenny which wasn't originally a centaur but made everything believe otherwise. Also she disabled the reality alteration to them while everyone else thought her situation was completely normal.
"So this thing can change ANYTHING!?" Eva gasped. "Yup" was Jenny's answer.
"Oh man that's sooo sweet! I could make my dick way bigger"
"Or I could make my boobs bigger, have a penis, or..." Eva snapped her fingers having an idea, then she pointed at Tyson, "turn you into my centaur lower half!" She grinned.
"Not if I turn you into mine first!" Tyson angrily pointed back at her.
"I knew you would say something like that" Jenny let out a small laugh, "so that's the reason why invited you two here!" Jenny typed a sentence on the computer very fast and pressed a key, making everyone's clothes disappear. "I'll give you two a challenge, I'll grant the winner a transformation with the computer like any of the things you just said, I'll even let you turn Jeff and Kat into parts of you!"
"And what do you have in mind big girl?" Eva winked at her.
"Well, since you're two and I have Jeff and Kat as my two sex organs, I'll set that the first that makes me cum will win! Eva, you'll take my cock as Tyson fucks my pussy!"
"Are you kidding? You're going to kill me with that thing!" Eva exclaimed looking at the equine cock.
"Yeah and I think this one won't make an effect on you" Tyson grabbed his penis thinking it wasn't enough to satisfy a giant and deep mare pussy.
"Okay, calm down you two" Jenny used the Chronivac to make a few adjustments to her friend's bodies, Tyson's dick grew to a size of an average horse one while Eva's vaginal track was modified to handle anything she shoved in the depths of herself.
"Wow!" Tyson barely could grab his new sexual organ with two of his hands.
"This is amazing!" Eva tested the change easily fitting her two fists inside her wet vagina.
"Don't get too excited!" Jenny crossed her arms, "those changes are temporal and will wear off after the bet" both friends nodded. "But now we can begin~"
As the herm centauress said they began the challenge, Eva put a small table below Jenny and laid on it spreading her legs with her crotch pointing at the horse throbbing trunk, "I'll show you how my insides taste Kat~" she chuckled. Tyson instead grabbed a stool to stand on it and rub his penis against the mare vagina before they started, "sorry Jeff, but a deal is a deal, I hope you enjoy this as much as we do" Tyson said while still rubbing his big human penis through Jeff's "mouth".
After some seconds Jenny gave the order to start, Eva grabbed the horse cock and quickly inserted it inside her as Tyson penetrated Jenny's rear. The competition just started.