The majority of the Demon Race's power is concentrated in the Northern Sea Cultivation Realm, where they have requested the Barbarian Cultivators to encircle and attack the Human Cultivators.
Whether the Demon Race can conquer the Qianyang Realm depends on whether they can exterminate the Soul Transformation Cultivators of the Qianyang Realm. Those below Soul Transformation are considered as nothing more than ants; the Demon Race does not care about Human Cultivators below Soul Transformation.
Once they exterminate the Soul Transformation Cultivators of the Qianyang Realm, the remaining Human Cultivators will be like fish on a chopping block, at the mercy of the Demon Race to be slaughtered.