Body & Soul - Do we know?

We assume, one human body has one soul , but how come the following questions didnt baffle us or we didnt look quite to answer them? The following are some of the commonly held beliefs almost in all religions which seem quite contrary to the one body housing one soul concept.

1. When an conception takes place at womb of the mother, this becomes like
.."two souls" ... within one human body.

2.When we see people who gets occupied by external Aavi(Spirit) also we realise
that, more than one soul can be present within peripheral of one human body.

3. When souls departs from a body, if the body left to lie as it is, we see millions
of "live" aspects surrection from the body within few days.

4. A drop of human sperm said to contain millions of active live's of which only one
of them ( for few unlucky (or otherwise) ones...couple of them) makes it to the womb
for effective coneception.