Spoolofwhool

Shallan told him to leave them behind, not murder them. I see no reason to think they would've just left them outside to die, especially considering there were no predicted storms until the end of the Weepings. Furthermore, I don't recall anything which showed that happening.  
Edgedancer does not have an applicable argument since no one in that area believed Dalinar when he warned them of the Everstorm, so they would have no reason to throw their parshmen out to die. 
In any case, I found something applicable.
 

Steel/iron pushing/pulling is a gradient scale on invested metals. The most invested they are, the weaker the steel lines, and therefore the weaker the ability to push it. Eventually, the object is so invested that it stops creating metal lines. Example of this is when Wax tried to view the bands of mourning. I don't think we've actually had an opportunity to see someone's viewpoint on pushing on a normal metalmind, but since the strength of metal lines is a function of how well you can push on something, Imy fairly certain you would see a weaker line for invested objects.
 
First nitpick. Shadesmar is a term for the entire Cognitive Realm, not just the Rosharan region, which is what I presume you're using it for.
I don't think metals on Scadrial are more invested than normal. It think it had to do with the nature of the planet and its influence over its cognitive realm combined with the fact that metals are a significant factor.
 

Mateform is the form optimized for breeding, but some other forms like slaveform (parshmen) can breed as well. Alethi breed the parshmen.

1. Nothing. Their spiritual identity is only gone while they're storing. Otherwise it's as normal, like any other feruchemical attribute (save memories.)
2. That's what Forgery does, in a sense. If you're talking about on your own, probably not, though it has been strongly hinted that the alternate self shadow that an Augur misting sees could possibly be used to change their cognitive, and by extension spiritual, identity.
3. The two possibilities I see are either that both identities blend and it could give the person access to any identity keyed item keyed to either identity or the tapped identity would override the current one. It might be that it depends on the strength of the tap. In any case, same thing as if a trueself ferring tapped an unkeyed aluminummind that someone else had made.