Here are some of the things I remember from the movie:
- The magical creatures were at risk - vague thought that they may be transdimensional.
- There was a lady - who may or may not have been in line for princess who was involved in a quest to save the creatures.
- There was a limited timeframe to save the creatures - maybe a week?
- There was a guy who was working with the lady.
- There might have been another lady helping out, who didn't appear until the end, who was the real heir.
- The main actors and actresses are all adults. I vaguely recall that at least one British actor was cast.
The action began with something getting loose and the protagonist being aware of the event, at some point the secondary lead meets up with her, reveals 'reality' to her, they go through some various trials as they work to save the creatures, maintain some balance?, eventually they succeed and all's well that ends well. It is a love story, feel good, fun, but with action and suspense.
I think it was late 1990's or early 2000's and it might have been one of those TV movies.
To differentiate it somewhat from similarly themed shows - it is closer to Sanctuary or Fantastic Beasts and Where to Find Them than Spiderwick Chronicles or Bridge to Terabithia.