I'm only going to answer this question:

In which month of pregnancy a soul enters into a new body (foetus)?

According to Garbha Upanishad, the soul enters the foetus in the seventh month:

सƯमेमासेजीवेन सयं ुƠो भवित । अƴमेमासेसवसर् पं ूणȾ भवित ।

English Translation: In the seventh month, [the embryo] comes to have the jīva (conscious self), and in the eighth month, it becomes complete in every sense.

I'm only going to answer this question:

In which month of pregnancy a soul enters into a new body (foetus)?

According to Garbha Upanishad, the soul enters the foetus in the seventh month:

सप्तमे मासे जीवेन संयुक्तो भवति |
अष्टमे मासे सर्व संपुर्णो भवति ||2||

English Translation: In the seventh month, [the embryo] comes to have the jīva (conscious self), and in the eighth month, it becomes complete in every sense.