Where's the soul?

A thought experiment. Accept as a premise, that there is such a thing as the common understanding of a soul, in the christian sense of the concept. Now fundamentalist christians believe that abortion is murder because god imparts a soul to the zygote at the moment of conception. But this comes from Aristotle, as far as I can tell, and although they were pretty advanced in ancient Greece, we know slightly more about how reproduction now.

1. What happens with mono-zygotic (identical) twins? I suppose the twin gets a new soul when the blastocyst separates. But what happens when the blastocyst recombines? Did somebody just die? Would I be met in heaven by the soul of my identical twin who died when the blastocyst recombined and they became my liver?
2. Fraternal twins can sometimes combine - creating a chimera. Here we have one person, from two zygotes, with two sets of DNA. Again, did somebody die there? Or is that one person with two souls?
3. If the embryos recombine after differentiation has begun, we can end up with a parasitic twin. The parasitic twin could be acephalous, so we have an individual with multiple limbs, organs etc. Again, did somebody die? 
4. We can also get bicephaly, one body, two heads. More and more are surviving birth and with good chance of normal lifespan. Is that one body and two souls? What about the cases where the second head is acephalous, in this meaning, without a brain. Would cutting off the head be murder?
5. The foetus can develop without a brain or a head, in this case, if the foetus goes full term, it will die as soon as the cord is cut. Does it have a soul? If a soul is reliant on a brain or a head, then an embryo would only get a soul after the brain has developed. If it is not dependent on this, then the removal of a parasitic twin's additional limbs would be murder. Switching off life support to someone who is brain dead would likewise be murder.
6. Up to and in some instances more than 50% of foetuses spontaneously and naturally abort in the first three months of gestation. So heaven must be full of people who were never born. Thinking about it, the greatest proportion of souls in heaven would in fact be from blastocysts and foetuses. 

Just applying the Axe of Reason.