IIRC from the gazetteer, The Eternal Order lost many followers after the requiem when The Eternal Order publicly declared that the populace's lack of faith was the cause of the fall of Il Aruk during the Darkest Night ceremony (as TEO (The Eternal Order) believed it to be the hour of ascension). That resulted in a divide between the general populous and The Eternal Order and the following for the Eternal Order has waned since. That said, I don't recall any mention of the followers now having to be inconspicuous in public, in fact, I believe it still mentions a few different festivals that are performed in Darkon that are likely part of tradition at this stage of the indoctrination (The last part is just my interpretation). Being the nationwide religion for so long would likely result in many people practicing the holidays (Festival of the Dead, Darkest Night, etc.) even if they weren't necessarily devoted to TEO faith. Throughout my reading, I never got the impression that they were a hidden and covert death cult and if you read their tenets, they more seek to impede or slow down the hour of ascension (when the dead will return from the Grey Realm to reclaim Darkon back from the living) than to cause it to happen, even though they believe its arrival is inevitable. The exception to this is a sect of the TEO within Il Aruk among the intelligent dead who wish to accelerate towards the hour of ascension, for obvious reasons.
The Faith of the Overseer is predominately in Martira Bay where it has a stranglehold on the faith of the population and has largely kept out both the Eternal Order and Ezrites as its religion is the only one with a temple in the city. Despite being originally a false religion established by the Kargat leader (Tavelia) at the time, it's dogmas greatly appeal to the populace and it is gaining in popularity. With the way that I remember it written in the gazetteer, I didn't seem as if either the Ezrites or TEO were going to change that any time soon.