Maybe the Singularity creates the aether. Or it is a natural occurrence that is a result of natural properties of the aether and its potential movement between worlds.

Only one. The Church says there is only one. I know that some societies believe in more than one deity, but I do not know much about any of them. Is your society polytheistic?

I am dead in some Fodlans, like Claude von Riegen's. I am alive in others, like my own. I am involved in a war, it is not a surprise that I am dead in some Fodlans. I see no reason to take it personally.