Surprises on Christmas Eve

Hi there. This is my first Ben 10 story. As you might see I wrote 'shonen-ai' as a warning. The explanation for this is that, even though Ben is a girl in this story, it is still 'shonen-ai' for me because both Pierce and Ben are originally male. I hope you understand what I mean with this ^^ I also listed the age of some of the people, but not all. It is a story for Christmas, but I decided to post it before the 24th.
there might be some grammar mistakes as my native language isn't English and I haven't found a betareader yet. If there any grave mistakes please tell me and I shall fix them. Hope you enjoy.

Disclaimer: I DO NOT OWN BEN 10!

Main Pairing: Pierce x Ben (female)

Side Pairings: Kevin x Gwen, Manny x Helen

Warnings: AU, Shonen-ai (boy x boy), probably OoC, Genderbender (If you don't like any of them, please press the back button NOW)

Age of the people

Ben, Gwen: 23
Pierce, Helen, Manny, Kevin: 24
Alan: 18
Cooper: 22
Grandpa Max: 73