I'd like to add my hunch that the 12 Ancients following Venat and help summon Hydaelyn are probably the 12 gods of the people of Eorzea. You can see them in the cutscene that immediately follows Anemnesis Anyder.

In other threads I've been calling them the Hydaelyn Convocation until we're given a proper name for them.

Furthermore, I feel that we aren't done with Venat either. As the Heart of Hydaelyn, much like Elidibus, says they will return and in a form of their choosing. So I guess the question remains who or what was Venat and what have they been doing?