Why would they have to be literal humans, and not figurative examples of the human condition for which people seek redemption from the suffering we experience? There's no reason they had to be historical, in order for them to be true symbolically.
The taking of the fruit, despite the express command from the Creator that it belonged to him and that they were not to touch it under penalty of death, was the event that set the entire human race on the path to sin and all it's awful consequences, including certain death. If these were not real people, then Jesus' coming to earth to offer to God the price for releasing Adam's children from the consequences of his actions, makes no sense.
Why call Jesus "the last Adam"? It is because he paid the price required by God's law...."an eye for an eye, a tooth for a tooth....a life for a life". Equivalency was demanded to make atonement. (at-one-ment) Like for like.
Adam lost his own perfect life and paid the price for his own sin, but there was no human on earth who could atone for the perfect life he took from his children. It was a lethal inheritance with no way to make the necessary atonement.
God stepped in and provided the price...the perfect life of Jesus paid the debt Adam left for his children. That is why Jesus' sacrifice is called a "ransom". (Matthew 20:28) It was the price demanded under the law of God to settle the debt and free the ones under bondage. (Redemption) This is something I was never taught in church. I was always told that Jesus died for us.....but never did they explain why. Once I understood the mechanics, it all made sense. I will wager that most in the churches today, still don't understand it.
This is why I believe that all the Bible characters were real people...why wouldn't they be?
Jesus could speak of them symbolically in the same way I do, and no meaning be lost. Do you not see that the truth of something is greater than the thing in itself, that the object we attach meaning to, is not the meaning itself? We are all Adam and Eve. They are us.
You seem to be unaware of why we (us) are in this situation, and why Christ came to offer his life. If these people were not real, then how does any of it make sense? How did humans become sinful and need rescuing from this inheritance that they had no way, on their own, to pay? (Romans 5:12)
Your scenario does not make any sense to me.