That's because you're listening to Altmer. To them Aedra means "Our ancestors" and no self respecting Mer would claim to have Lorkhan as their ancestor. To man on the otherhand, Aedra and Daedra is closer to self-sacrificing gods and selfish-demons.
And man's version is the most correct. The dunmer also have a different view of the daedra too, pretty manish. Stupid altmer.
You got it backwards. There are three dementions, layered like this,
Mundus - Oblivion - Aetherius
Nirn( the planet that has Tamriel) Daedric Realms The soul sleeve (the recycling center for souls)
The Aedric Planets An island thrown by Mehrunes Dagon into oblivion The root of all magic Masser and Secunda Gaiar Alata (associated with Dagon as well)
The chimera of loneliness or something (few lore refrences)
That's at least how I understand it.
I'd say not quite.
I figure it to be Mundus is mortal universe and things associated with it. It's center plane(t) is Nirn, with the aedric plane(t)s and Shor's holy flesh orbiting around. It's also in the center of the universe.
Then you have Oblivion. Inside Oblivion, you have the 16 princes orbiting around.
Last, there's the Aetherius, where the Magna-Ge reside; those who fled and created the holes in the sky known as the stars, with the biggest being Magnus' as the sun. Because of these holes, magic leaks from the Aetherius.
In short Mundus (aedric planes, Shor's flesh (the moons) and Nirn)-->Oblivion (the 16 realms/princes)-->Aetherius.
The dreamsleeve is the place where mortal souls go when they die to be wiped clean, and begin completely anew. In contrast, the daedra also sorta go through the same thing, except they're completely aware of what's going on, and they don't have the memory wipe. They can also come back when their lord picks them out, or they swim fast enough. Mortals have a lottery system.