The hundreds of fantasy books I've read all have more than one storyline, but almost always a main character. Sometimes this is immediately apparent because the story is written in the first person, but most writers use the third person. In that case, it's harder to discover because someone has the point of view in each storyline. Keep in mind that you should limit the number of perspectives. If you have four storylines (in the trilogy), then four perspectives are no problem. You decide how many storylines there are in your story. I'd like to elaborate on this in more detail.
The problem with storylines is that the reader constantly has to switch back and forth. A fantasy story is Good versus Evil, and there may be countless scenes with many characters playing a role in your story. Many fantasy stories take place in multiple countries where different people live. If you have eight storylines, which will converge more and more in the final part of the trilogy, you probably also have eight perspectives. That's really the maximum. Four perspectives are easier for a reader to follow than eight.
Magic always appears in fantasy stories, but you can't fantasize about it endlessly. Readers don't like it when, out of the blue, someone suddenly becomes able to do something, simply because it's illogical, too easy. If there's a problem, then suddenly, at just the right moment, a fantastic solution appears. That's not how ordinary life works, and that's not how magic should work either. For example: a character in your story suddenly becomes a magical archer whose every arrow hits the target. The reader will rightly wonder where that magic suddenly came from. You have to provide an explanation. They received magic from a god. Fine, but how? Did that god give them the bow and arrows? It's possible. So that god is able to appear to someone and give them something material. You have to maintain that throughout the entire story, which spans three books. Does that also apply to other gods? Can they also give something to a mortal? Or not? Why not?
With the example above, I want to emphasize that you shouldn't take fantasy too far, and that everything demands a, often brief, explanation. And you really have to be consistent. If someone is an exceptionally good swordsman in the first book, they'll still be so in the final part of the trilogy, or something must have happened that explains how and why they're no longer so. That's entirely possible. I'm returning to what I wrote earlier: everything needs an explanation, or it must be clear to the reader why a change has occurred. Sometimes you can explain that with a single sentence, assuming the reader can fill in the rest themselves, and further explanation isn't necessary.
Next time, the final episode.
Rolf