Hi, Airciser, welcome, and great questions! To answer them:
Malor, Barathus, and Carcus are the Farlandic names for the Abyss, Hell, and Gehenna respectively. The evil gods Vornoth attempted to subsume into the Book of Seven are Soggoth, Lagur, Bemit, Yorsot, Tormossh, Nij, and Grlarshh. Grlarshh, however, managed to escape-- the first six were subsumed and destroyed forever. So the Book of Seven is actually more like the "Book of Six," which explains why the Dweller took so long to use it to create the Lords of Sin-- the book was incomplete. We assume that she eventually figured out a way to complete it. The story is told here:
http://www.farlandworld.com/genesis.html
Salystra is a powerful demon lord (or lady). During the Godswars, a piece of Malor, the domain of Salystra, was sundered from the plane and ended up traveling down the Astral River to the Maelstrom. Finding herself about to be destroyed by the limitless energy of the Maelstrom, Salystra enclosed her little chunk of Malor in a force shield, but in doing so, she trapped herself in the Maelstrom. She exerts the majority of her energy to keep herself from being destroyed, but she is able to use what is left to communicate with the drow, to send them cleric spells, etc, and to send her agent the Serpent of Twilight to Nurion to try to arrange some way for her to escape to Nurion itself. The relevant link is here:
http://www.farlandworld.com/droworigin.html
Hope that answers your questions!