Hebrews 2:14 Forasmuch then as the *children* are partakers of flesh and blood, He also Himself likewise took part of the same; That through death He might destroy him that had the power of death, that is, the devil:
We are told what took place at the conception of Christ, His Soul/Spirit was placed in Mary, even recognized by John in uterus, as is the same with the conception of any child through man and woman. Our Father does not require of us to do anything that HE Himself was not willing to do as well. Big difference is that our Heavenly Father was, is, and will always be perfect, while not so of we children.
Even in the 'sour grapes' proverb of Ezekiel 18:4 Behold, all souls are Mine; as the soul of the father, so also the soul of the son is Mine: the soul that sinneth it shall die.
This sure does not sound like a soul factory being described if the Heavenly Father is stating that all souls are His.
So yes each soul has the *free will* to be born of woman and pass through this flesh age. And NO the unborn are very much flesh bodies which is the vessel or body the soul inhabits as that is what gives that body life. (As described of Adam it was not until the breath of life = soul was breathed into his nostrils was Adam a living being.)
IICorinthians 5:6 Therefore we are always confident, knowing that, whilst we are at home in the body, we are absent from the LORD:
7 (For we walk by faith, not by sight:)
8 We are confident, I say, and willing rather to be absent from the body, and to be present with the Lord.
Why not? I don't follow. All souls are His because He created them and installed them.
So yes each soul has the *free will* to be born of woman and pass through this flesh age.
I'm sorry but I just don't see how what you're saying supports that idea. People just do not choose to be born. The implications are also disturbing. For example, can it be said that miscarriages are babies who chose not to be born?