I'm looking for the name of a fantasy series that I read around a decade ago. I know it left a strong impression on me because I remember thinking it was a great read at the time, but I've lost most of the plot details and can't remember the title. What I do remember is that:
- The book was written for children or teenagers
- There were three protagonists around the age of the audience: two boys and one girl
- The series involved the children repeatedly visiting a fantasy world through some portal they had access to in our world; they kept this a secret whenever they returned home at the end of an adventure
- Each of the kids was changed during some of their adventures, and the changes manifested in the real world. One of the boys learned magic, one of them was bitten by and became a werewolf, and something else happened to the girl (I don't remember perfectly but I think she may have become a ghost?)
- I specifically remember the main protagonist showing off his magic to the other characters in the real world by turning a glass of water upside-down and instantly freezing it so nothing poured out
- They worked to help a recurring character in the fantasy world, a princess around their age. I remember an association between her and the color white, and I think one of the protagonists had a crush on her
Those are all the details I can remember for now, but if I think of anything else I'll be sure to add it. This was years ago (~7-10, though it might have been written earlier than when I read it) so I don't expect all of the details to be exactly correct.