As mentioned in the OP, many of the stories in Genesis are not historical and were written to explain the geopolitics of the day.
A fantastic example of this is in the story of Jacob and Esau grappling for first birth.
(1) Medically, two babies cannot grapple to come out first in a narrow birth canal. Indeed, they almost always not born hands first
Hands first – Babies are generally born head first (cephalic presentation), with the baby’s hands positioned alongside its body, pressed in by the birth canal, toward the direction of its legs. Less common are the breech presentations (3-4%). In rare cases (0.1% incidence), an arm or both arms can present together with the head or buttocks (compound presentation). But, to the best of my knowledge, babies never emerge with their arms extended forwards.
(2) The author of the story of Jacob and Esau, and Zerah and Peretz was almost certainly male, familiar with animal birth but not human birth ;
The male authors of these passages assumed that human children were born in the same way as farm animals—births that they would have seen. In standard births of cows, sheep, and goats, as well as horses, camels, and donkeys, the hooves (the tips of the forelegs) are the first parts of the body to emerge from the womb. The hooves precede the tip of the newborn animal’s nose and its mouth, which are thrust forward by the pressure of the birth canal.
In difficult births, when the animal refuses to come out of the womb, a farmer will tie a rope around the forelegs, which are sticking out, and pull the animal out. The pulling action brings the forelegs out first, while the head retreats somewhat, emerging from the birth canal only after the legs have fully emerged. Ancient farmers and shepherds likely employed similar methods to assist an animal with a difficult birth, and this would have further reinforced their conceptions about the sequence in which limbs emerged during birth.
If you are unfamiliar with the story of Zerah and Peretz, here it is
Gen 38:27 When the time came for her to give birth, there were twins in her womb! 38:28 While she was in labor, one of them put out his hand , and the midwife tied a crimson thread on that hand, to signify: This one came out first. 38:29 But just then he drew back his hand , and out came his brother; and she said, “What a breach you have made for yourself!” So he was named Perez. 38:30 Afterward his brother came out, on whose hand was the crimson thread; he was named Zerah.
Do you believe that during the birth of Zerah and Peretz,
(1) Zerah stuck his hand out first
(2) Crimson thread was stuck around the hand (like an animal to assist birth)
(3) That Peretz and Zerah then swapped places in the birth canal such that Peretz ended up being born first???