Questions for Christians

Would the newly created people be inherently sinful? We are because Adam and Eve sinned. Would the children of those people and Adam and Eve be half sinful?
I know lots of Christians accept that the story is a myth, but with no garden there is no initial sin, and with no initial sin done by humans there is no need for salvation. If we are made inherently sinful, that’s God’s fault, not ours.

I’ll assume the OP is asking all of these questions in good faith:

  1. He married one of his sisters. Adam & Eve lived a long time and had many daughters & sons other than the three sons mentioned. The Bible tends to focus on the most important figures in the story and ignore the others.
  2. If by confession you mean repentance of his sins & acceptance of Jesus, then yes. All of Hitler’s sins would be forgiven and he would go to Heaven.
  3. I’m not a Catholic and I don’t believe Mary was sinless. On a side note the Bible tells us she had other kids with her husband after she had Jesus
  4. The Bible doesn’t say only humans were given free will. It describes Satan and other angels choosing to disobey God.
  5. The answer is related to free will. Adam & Eve were created to rule over the earth and do with it as they pleased. In spite of God’s warning that it would bring suffering & death they chose to disobey Him. The consequences impacted them, their children, and everything else alive on the planet. God didn’t undo their mistake because free will.
  6. Free will is the big question IMO and I’ll do my best to address it here. But before getting into the free will discussion, it’s useful to understand Adam & Eve actually WERE created with the ability to have free will and not sin, with a single exception (eating the fruit). In their original state they could have murdered, committed adultery, had sex with animals, etc and it would not have been a considered a sin. It was the act of learning what was right & wrong (by eating the fruit), in rebellion to God’s command, which caused them to be thereafter judged by God’s standards and be held accountable to keep them. I suspect if they had refused to eat the fruit God would have eventually given them permission to eat it anyway. And they would have learned good from evil but without the desire to commit evil or any of the other consequences.

Let’s get into free will. Yes, the fruit was a test. Apparently God considers free will to be an extremely important component of humanity. It’s so important that He’s willing to risk sacrificing everything else to avoid losing it. And so He gave Adam & Eve a way to choose to reject God (eating the fruit). As I mentioned before they could have done any of the things considered sinful today and it would not have been considered sinful or a rejection of God. When they ate the fruit the act was a sin (God told them it was wrong) and it became possible to sin, because they now knew which of their other actions were and weren’t evil.

You didn’t ask it but a related free will question I hear is, “Why didn’t God stop them from eating the fruit?” And the answer is, if we aren’t free to make mistakes (or take actions which others don’t want) we don’t actually have free will. Say Adam & Eve wanted to eat the fruit, but God stopped them right before they ate it. He explained why it was a bad idea and sent them on their way. Then this happened the next day and the next. For their own good He never lets them eat it. Did they ever have a choice to eat the fruit?

From here.
Who Were Adam and Eve’s Children? How Many Sons and Daughters Did They Have? | Bible Study Tools

When it comes to the origin of original sin, the story of Eden is both a tale and the truth.

Does it? I thought that whole “fallen angel” thing was basically Elizabethan bible fan-fic.

I’m assuming you mainly want to hear from Christians who interpret the Bible literally rather than metaphorically? Cain didn’t marry his sister because he didn’t exist. Every religion has its myths, and I assume they pretty much all have adherents who don’t take them as history)science.