I only read Action Comics and I'm confused as all fuck
How is Clark dying? Who's this double? WTF is happening, pointless me reading this if I need to read another 3 superman books
Clark is dying from all the this that's happened in the Superman books, Justice League and JLA.
The not-constantly-on-fire double is the pre new 52 Superman, put on our Earth by Telos after the events of Convergence, where he and Brainiac had a bunch of people from different timelines and universes fight each other.
The constantly-on-fire double IS THE WHOLE MYSTERY OF THAT ARC.
Also, yeah, it's one story across 8 issues of four books. There's numbers on the covers for ease of following.