So... I'm trying to put the various pieces together from your story, blog, and various other comments, and I think I'm starting to get a clearer picture of what's going on!
1) We know Uther originally had 2 twin daughters (whether they were his own flesh and blood is another matter).
2) We know that Silva and Aurora look alike.
3) You've mentioned that multiple shrikes/sirens could be stationed at a Blackmoorian stronghold simultaneously.
4) We know that Blackmoorian soldiers could have their "souls" transferred into warforged bodies
5) We've just seen Aurora be reborn - with her memories (mostly) intact!
Therefore I must conclude that we are dealing with some variation of Cylon resurrection technology here

The assumption here is that Silva and Aurora are unique in some way - at least in regard to other warforged. They could be the pinnacle of Blackmoorian technomantic wizardry, or they could have been the model that lesser warforged were based on. If the former, then at some point the real flesh and blood girls were transferred into warforged bodies at some point after they first emerged on the scene. If the latter, then I'm not sure where they came from. The first thought would be that they came directly from the City of the Gods, but somehow they are tied to the Fey Queen...
Hopefully I haven't jumbled too much of this up. At any rate, I'm really enjoying the direction this has taken!