Fair enough, but even completely fictional characters are based on the author's experiences and previous literature (which there wasn't much of at the time and even what did exist wasn't very accessible due to literacy rates). This can go back and forth forever and unless a Greek history scholar comes in idk if there's gonna be a real answer, I was just proposing one possiblity

Nothing, I haven't researched Greek archeology but I know these stories are usually word of mouth things passed down and embellished over generations. It's pretty safe to assume that gods didn't actually exist back then but these stories must have had some origin so I think it's reasonable to assume they're at least loosely based on real people

In the stories. It's not unlikely that those stories were based on regular people who did incredible things in their lives, and were remembered as demigods after their deaths like the post says