God directly causes the pregnancy of ALL women, AB.
Wait… wait.
I don’t think you mean what you wrote – or maybe, that you mean something subtly different.
We believe in primary and secondary causation. God caused the creation of the universe (and therefore, the first humans), and humans – as moral agents – cause events to happen. The fact that humans cause an event does not imply either that God directly caused the event nor that God approves of the event.
As you point out, when a baby is conceived in an adulterous relationship, this does not imply that God endorses that relationship or that God caused the pregnancy.
Therefore, AB’s assertion that the events in the Jacob/Leah/Rachel narrative
prove that God approves of polygamy is patently false.
However, it also means that your statement which I quoted is itself false. When a couple causes a baby to be conceived, God
participates in this act through the creation of an immortal soul. In this way, we
cooperate with God in the act of procreation. However, that still doesn’t imply that God necessarily approves of or causes the pregnancy. Rather, having given us the gift of the ability to participate in procreation, He honors His gift when it is utilized by humans.
Therefore, AB’s case falls apart; all we can infer about God’s will, via the pregnancies of Jacob’s wives, is that God willed humans to cooperate in the gift of procreation and that God willed us to have free will in the way we make our choices. Period. Nothing further.