The main reasons I imply that the gods all belong to the same pantheon are that: a.) the first post in the OOC indicates a single pantheon, pantheon singular and b.) the Bastion of Light is a fire that represents the lights of all the gods, implying that their powers combined are interrelated and represent a unified force of order in the world.
While it can be argued that they are from separate religions, I'm given the impression that they originate from the same religion and that cults and sects specifically devoted to specific deities are regional—for instance, Faerthus is extensively worshipped in Cyndaria, but in other regions may not be as heavily emphasized despite his importance. This is analogous to Hinduism in the real world and how Hinduism defines important gods but acknowledges the existence of lesser deities and a pantheon of gods that are as numerous as the stars in the sky and how Hindus may express devotion to a single god while acknowledging the presence of others, especially in their rituals, beliefs, and practices. I also believe that they might originate from the same pantheon because it is written in the lore that Ansur brought the gods (plural) to Ansus, which is an important fact to note because it leads us to believe that Ansur did in fact recognize multiple gods in the same religion and that the people who he led to Ansus simply had patron gods that they worshipped above the others, with varying degrees of devotion to the gods as a whole.
But the afterlife, as presented to Ellarian, Altim, and Ansur, is extremely similar, and that in turn makes it seem that the afterlife they are presented with is the same. It could be that the believers themselves merely see what they want to see or that the gods do rule over the universe together but have separate domains into which they admit their most devout. It could even be that the realm the legends themselves entered after death was merely temporary under the notion that it lacks time and is merely like an egg before their rebirth because their souls never fully left the mortal world. The idea that gods have separate 'pocket dimensions' and 'personal planes' has nothing to do with what religion they belong to or whether or not they have an interaction with other gods.
But the world itself begs that the gods interact in some way. Even in the lore of our characters, it's given that divine intervention is a common theme, but that divine intervention is universally recognized across Ansus; the people of Ansus know that there are other gods and do not deny their existence, hence the likelihood of a common religion. Furthermore, that divine intervention has an effect and a consequence in the physical world. The entanglement of their controls over the physical world, therefore, begs that the gods must interact and exist together on some level. In better words, they all have an effect on the same world; therefore, they all must exist in that same world.
Another thing, how do we know that science and study are completely separate from religion and myth in this world? This world may have not experienced that sort of divergence which exists in our own, wherein some time ago science tore itself from religion to become a separate field unto itself. It could very much be that in this world, science and religion aren't entirely separate. Likewise, we could suppose the opposite. But we don't have definitive history that suggests that religion and science are separate, nor do we have definitive history that suggests that the gods come from separate religions. If anything, religion and study could be very close, and multiple sects/denominations could have emerged from the same religion in which the pantheon of all the gods are contained, these sects all having common tenets but devotions and commitments to different gods, all the while submitting to the truth that all the gods exist and have sovereignty.
TLDR: I don't think there are different religions, but I do think there are sects or schools of worship of a single, polytheistic religion that is similar to Hinduism. That religion traces its source on Ansus to Ansur, who was born of a god, very well could know of the other gods, and could hold to the belief that they belong to the same religion.
What I intended to create was a structure for that religion's pantheon based around the cosmology of this world, which has yet to be fully determined.
A lot of our conclusions so far are heavily deterministic and imply that the roots for many of these ideas exist in the first place when in reality, the evidence that we draw from could also be manipulated easily to show that the other opinion could hold equal truth, due to the lack of a canon that has established either opinion as true.
Edit: But I don't know. I want to avoid trying to apply paradigms and philosophies that, despite making perfect sense and being rooted in fact in the real world, do not hold so well in a universe that is very clearly fantasy, especially when it's obvious that this universe we're taking part in is separate from our own and is removed to a degree from the logic, realism, and rationale of our world. I can't make the claim that any one of us is particularly wrong, and neither can that same claim be made against me, especially since, you know, this is fantasy, and the world, in our case, is very much up for interpretation. I just kinda wish I didn't have to worry about the alternate religions or the heterodoxi-whatchamacallit because this world doesn't have to be 100% firmly bound by real world rules.