In most comic storylines, Jimmy Olsen isn't a guardian. He's more often involved in reporting and assisting Superman rather than having a guardian role.
I'm pretty sure it's not real. There's no concrete evidence or reliable source to confirm its authenticity. It could just be a story someone came up with for entertainment.
The batman v superman story is complex. Batman, who has been operating in Gotham, becomes concerned about Superman's unchecked power. Superman, on the other hand, is just trying to do what he thinks is right for the world. Lex Luthor manipulates events to make Batman target Superman. However, as the story progresses, they realize they need to work together against a common enemy like Doomsday.
In the 'batman v superman graphic novel', the story mainly focuses on the conflict between Batman and Superman. Batman sees Superman as a potential threat to humanity due to his great power. Superman, on the other hand, is just trying to do good but is often misunderstood. There are also other elements like Lex Luthor's schemes to fuel their enmity and Wonder Woman's appearance which adds more depth to the overall narrative.
The main characters are Batman, Superman and Lex Luthor. Batman is the Dark Knight from Gotham. Superman is the Man of Steel. Lex Luthor is the villain who causes a lot of the problems between them.