Do you know this children's series?

Okay, so I remember this book series (chapter books, about 100 pages long) from when I was about 7 or 8. They were set in the middle ages, and the heroes were these 3 kids, 2 boys and a girl (Who pretends to be a boy around the adults, since they are in a school for knights) The main character has red hair. One of the titles was called "Countdown to 1000". There was a crossover between these books and the Zack Files, With zack coming back in time, and the kids thinking he's a demon. I also remember the main character had a pig that spoke pig latin, and that the principal of the school loved money. I know that these are very vague details, but maybe one of you knows something about these books. Thanks!