Well, basically, the Ancients were all knowing. They did not wish to share their ways with lesser beings because it would disrupt the balance of something. For whatever reason, The Progenitor or All-Father, shared ways with those beyond the dwelling of the Ancients.
So based on that part, The Ancients are a council, prob of equivalent leveled Gods.
In this world, knowledge of certain magic or w/e is considered power, those in power are separated by those who have no power by a veil.
The Progenitor prob broke a sacred rule, and got banished, and to add insult to injury i guess that him and everything he had as an Ancient, he lost.
...my guess is that while he had betrayed the Ancients, those actions of his led to the birth of individuals with Ancient Knowledge. So they are demigods, not of birthright, but of self-achievement. this makes sence, because they are called "pretenders" in the story, and demigods do not need to "prove themselves worthy" in most myths of our history.
...after The Progenitor was cast down, i think this cuz i view "Deep Places" as deep space, like the cosmos and w/e
...he wasnt prisoned, just laid low, he was weakened, a lot!
...Im guessing that the thing in the prison is a devil, or demon, not relevant to the mythology....