I Feel like Ahsoka is in another time at the moment, and thus not present during the time of the OT. The place she entered through that door looked like the temple she fought Vader in (I could be wrong there), but, much later (I feel).
As to the Ahsoka/Ezra/Kanan Mortis thing, I don't really feel like the entirety of the force is represented by those three. They are all pretty light sided.