Olympians in the Marvel Universe

[Slimybug]

First off, no spoilers for the Eternals movie. Yes, I'm talking about THAT spoiler!

I wanted to gain some clarity on this, considering the new Eternals film coming out. Mainly, I'd like for someone to correct me if I'm wrong on any points. I have thoroughly read the original run of The Eternals and The Thanos War arc, so I'm basing this on that.

So one of the first instances of Olympians in Marvel Comics was the appearance of Hercules as a main superhero in Journey into Mystery Annual #1 (1965). I'm not sure how much they ever got into his backstory, or family, like Zeus and all that.

Thanos was then introduced in 1973, and his full origin was explained in Captain Marvel #29 (Nov.). This delved into Greek mythology, stating that Cronos, rather than being deposed by his son as told in Greek Myth, actually had an experiment accidentally turn him into an incorporeal, cosmic being. Then his son Zeus took over and another of Cronos' sons, one more than is told of in myth, A'Lars, also known as Mentor, was banished from Earth, eventually coming to the moon Titan, which was ravaged by war and had only one survivor, a woman named Sui-San. A'Lars and Sui-San were married, and had two sons, Thanos and Eros. Apparently this was long enough ago that Eros still managed to come to Earth and work his way into the ancient Greek Myths. What's not ever explained is that, if Sui-San was the last survivor of Titan, how did it ever regrow? Apparently it grew into such a booming population that Thanos, as it's prince, was rich enough that, after being banished from it, he could grow an army of mercenaries that was a serious threat to the galaxy.

So I guess my first question is, since this was all supposed to be in the same Marvel Comics continuity as Hercules, did it jive at the time with the version of Zeus already presented, or was there some major retconning needed after this.

Then, in 1976, the Eternals came into the Marvel Universe, presenting Thena as the daughter of Zeus and the basis for the mythical character Athena. As far as I understand it, Eternals wasn't originally intended to be a part of the MU, so when they later decided it was, they had had to retcon this Zeus to be the same one that was both father of Hercules and uncle of Thanos. This also means that all Olympians are actually Eternals. I don't know if it's ever been retroactively explained why Hercules and other Greek figures that have become a part of the MU weren't included in the giant Eternals meeting in that short-lived series.

Is this all correct? So Thena and Hercules are actually siblings and cousins to Thanos, who is Half-Olympian/Eternal, and Half-Titan?