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.
Most of the time, yes. The entertainment industry is rife with false rumors, and Keira Knightley is no exception. These sex - related stories are usually part of the tabloid's strategy to create a scandalous image. They take a small incident or even make something up out of thin air to sell their stories. Keira Knightley is a respected actress, and these false rumors are an unfair part of the price of fame.
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.