Question

The narrator can be any of these characters: major or minor, protagonist or antagonist.

Answer 1

True, the narrator can be all of those things.  Some examples include the following:

Major Character who's the narrator: Hazel Grace Lancaster in The Fault in Our Stars

Minor Character who's the narrator: Nick Carraway in The Great Gatsby

Protagonist: Esther in Sylvia Plath's The Bell Jar (narrated in 1st Person POV)

Antagonist: Amy Dunne in Gone Girl by Gillian Flynn