If you can contact the authors and ask under what name they want to be credited, it won't hurt if you do. In your case, I'd suggest contacting the authors through the "discussion" page of their user accounts.
If you don't get an answer, your only option is to just go with what you have. And it's a fairly safe assumption that if the author already signed their work with the name they used, then it is the name under which they want to be credited for it, or at least are fine with it.
It's the author's right to sign their work with their legal name or a pseudonym, and their choice should be respected. Sure, we're more used to pseudonyms for creative works than in the academic sphere, but it is possible to come across an academic work signed by other than the author's legal name. I know of a transgender scientist who published articles in academic journals under a name she wasn't yet allowed to legally assume at that point of transition. Not really the same situation, but technically, her real name (the name she identified with) would be understood as a pseudonym.
And sure, it is going to seem unusual when the pseudonym is clearly not anyone's legal name but an internet username. But that doesn't make it wrong. What would be wrong is if you didn't credit the authors properly. So go ahead and give credit to Slashme, Patrick J. Lynch and Fvasconcellos.
It's perfectly legit.