I will update information as you learn more about these religions.
These Gods are held throughout Altera, though they are most commonly worshipped in Jenin, where the religion originated. The religion is a patheon of fifteen facets of The Heart, each God representing a college of magic. The religion holds that all magic originates from these Gods, and each facet has its own sub-culture of worshippers with their own rites. The Gods are listed here, at this link.
The Christosians believe that there is one true God, and that his representative on earth is a man named Christos, his one and only son who died long ago for the sins of man. (Sound familiar?) This religion is very popular in Gardjief. There are several variations on this theme in Gardjief.
The God Under the Mountain - the one true God, according to the Imperials. The entire Imperial social structure is based on the religion, as God laid out the structure for them under Caissius Caladore, the First Emperor of Men.
A small faith in The City, its roots stemming back to the beliefs of some indigenous desert tribes. It describes how Hocma, a mortal man, rose to Godhood with the help of three angels who banished The Creator and The Enemy, who had begun using humanity as a wager of their own power. Possibily a derivative of native faith, mixed with Christosian beliefs.
A dead religion and civilization. They held that Tristitia, a nature Goddess, ruled over them benevolently and guided their civilization until a Prophet appeared, and captured the Goddess inside six stones of power, corrupting the land and it's people. With the Goddess's dying breath, she destroyed her people with a massive comet.
The religion focus's on worship of Elerebrithriel, one of the Fifteen who guards Haissa, a spiritual prison for the sinners of the world. Those who follow this religion often seek the vast powers that The Dark Father lends to his disciples - but the cost of these powers is often high. So far, you have found three temples built for this Deity - and destroyed two of them. (The Sunless Citadel and Eastrocke were both destroyed by your efforts. The third, yet standing temple is the Arbiter's Temple.)