In my early teens (in the late 90's) I borrowed a series of fantasy books from the public library. I remember getting annoyed when the next book in the series wasn't in, so this series has at least 3 books. The story line is still very vague to me: a group of children is transported to different worlds, I think 2 ended up in a world with highly advanced technology. Another, a boy, in a medieval type of world with swords and magic. His name was Rohan (or Rolan, Rogan, Rodan or something in that same vein that starts with an "R") and he ends up becoming The Knight of the Red Rose or has something to do with a red rose. And if I remember correctly, all these worlds are somehow connected to each other.
I originally read this series in Dutch but I'm pretty sure it's translated from English
Please help me out with finding this fantasy series. I never finished it and it has been bothering me lately.