I am writing a YA fantasy. There are three main characters, but the plot was entirely designed around Character #1 and his journey. Character #2 and Character #3 are with him for most of said plot. The problem arose when I began delving deeper into the second and third characters. I began to find both of their worldviews, personalities, and backstories just as interesting as the main character's. Character #2 might even have a more interesting arc than Character #1. (I should clarify that I don't want to take away Character #1's perspective either; he's interesting too, but he isn't giving me issues.)
I realized very quickly that I wasn't going to be able to showcase nearly as much of these interesting characters if I didn't write from their perspectives (This also has the added benefit of showing what information each of the character's have and what they believe, two things with a great deal of discrepancy between characters).
Some solutions I've come up with (and the questions to go with them):
I could just give in and do a three-way split between all of their perspectives. The main issue here is that Character's #2 and #3 might be far less interesting since the plot was designed for Character #1. Anybody have any experience with last minute POV additions? What are some pitfalls to look out for? Is there any way to do this and still make it feel like Character #1 is the main character?
I could attempt to have Character #1 discover their interesting backstories and try to portray their arcs from his perspective, but I'm not even sure how to do that. What are some strategies for getting my side characters to give up their backstories to my main character?
The one I'm leaning most toward is a sort of compromise: I could write primarily from the perspective of Character #1 while just occasionally throwing in chapters from the perspectives of his two companions. I don't know what the cons are to this, but I've never seen anyone do it, so I assume there are some. Will this cause any issues? Why isn't this often done?
Any additional solutions or answers to those questions would be appreciated.