The elementals may amount to the Mawsworn trying to quell rebellious flames from or for use in the forges of Torghast. They’re unlikely to be from the Elemental Plane; that realm is specific to Azeroth, as it was created by the titan-forged (specifically Ra and Helya) to contain the planet’s Elemental Lords, so it’s not an “external” realm of existence like the Light, Shadowlands, Void or Twisting Nether. As a pocket dimension tied to Azeroth, it’s technically part of the Great Dark. As far as has been shown, the elements as a general “presence” seem to be an omnipresent and fully integrated with reality rather than one of the “big six” opposing cosmic forces that are largely segregated to their respective realms and trying to influence the Great Dark and Twisting Nether between them. Localized situations like Azeroth’s can result in certain elementals striving to overpower each other, but by all indications so far when the elements aren’t being abnormally affected by something else, their natural state is to seek balance with their surroundings and each other.
In a way it comes across like while the universe as we know it is a product of Light, Void, Life, Death, Order and Disorder in relative balance, the elements are sort of the universe’s own manifest internalized mechanism for seeking balance.
The night fae and kvaldir in Torghast are indeed strange, since the former are also hostile to the player for some reason, while the latter should logically be allied to the Jailer via Helya. Unless it’s meant to suggest that by joining the Jailer she may have handed her own minions over to him for processing into more weapons and Mawsworn, making those kvaldir unwilling “sacrifices” who are fighting back.