Libel and defamation will be hard to prove without Lloyd first finding and winning a lawsuit against "Marko."
But if he is claiming that Marko doesn't exist, then I am assuming he would be suing K&M for defamation by claiming that they used this imaginary person as a vehicle for making defamatory statements. Kim and Mikey may have to prove that Marko is real and that he made the statements in question (and if they can do that, then Evans could conceivably proceed with action against Marko).
Mind you, if he wants to initiate legal action against them, there are likely to be a few hurdles. Such as filing suit in a jurisdiction halfway around the world, and having to decide if it's worth it for what may end up being a very small judgment. And the possibility of being deposed, or having his wife deposed. And the chance that he might lose. And so on. In the USA, filing a lawsuit is very easy. Winning... that's a bit more complicated.