Bleedman stated that all his comics are in different parallels. Fusionfall as well would be just another universe. However, below I have connected them all anyway - ANOTHER parallel universe if you will. First I will use Fusionfall's map to connect them together. I could not find a truly accurate version of the map, but those that have played the game will know where these locations are.
1) The floating lands of Sugar Bits are above Sector V. This is why Stickybeard frequents the area - the sugar in the area is a goldmine. People should have listened to Knightbrace, cavities really are monstrous.
2) A Portal to Hell/Heck/The Netherworld/Limbo/Purgatory (Really, why are they all in the same realm? Seriously?) is in the large forested area on the right side of the map (the Holiday portals and this portal are all in the trees).
3) The Ice King's iceberg in Fusionfall is one of his many homes and it isn't his main one. The ocean behind him is where Flapjack's islands are.
4) The Ghost Realm is extremely close to but separate from Halloween Town and "Hell". In another way, it is also connected to the Nightmare Realm of SB.
5) The Nightmare Realm is connected to Ever After's realm in a way different from the floating lands of SB.
6) Heaven was once directly connected to Hell but we know what happened there. That area is now completely sealed off by quantum means.
Now for the timeline:
1) PPGD is the first of the timeline. End of Elementary for the PPGs, Dexter, etc.
2) Always plagued by his nemesis's death, Dexter eventually finds a way to go back in time and save Mandark at the last moment. Because he was so distraught, he and Blossom easily and eventually cut it off by silence.
3) The cast is now in Middle School. Dexter decides to finally test his time machine on the future and Fusionfall happens. [The mother in SB dies right after everything is fixed.]
4) Everything back to normal, Dexter is reprimanded (somewhere by someone somehow very important [I know this is a gap]) about altering the natural course of events and is banned from doing time travel ever again. This is why he doesn't foresee the events of GT.
(Extra) DCUO happens right before GT's events. Seriously, humans and their time travel... *shakes head*
5) Gene from SB - because of the events of SB yet to be revealed - eventually gives in to the innately demonic part of him. Before the full takeover, he decides to disguise himself as a normal person and enter a high school in the human world. It is here that he and Blossom hook up. Later he gives in and becomes the HIM of GT.
There ya go. Did I miss anything? :0
Oh, and the Invader Zim comic happ- You know what, it's not significant enough to even place xD