How did Red Skull determine who someone's parent was on Vormir?
Basically the title.
In IW he calls Gamora the "daughter of Thanos" who obviously isn't her biological father, presumably just because she spent more time being raised by Thanos than by her biological father.
But then in Endgame when Clint and Nat go to Vormir he calls her "daughter of Ivan" even though she never even knew her biological father's name and would have thus spent more time with Alexei growing up (albeit still not much time, but at least she remembers him).
Why so inconsistent?
In IW he calls Gamora the "daughter of Thanos" who obviously isn't her biological father, presumably just because she spent more time being raised by Thanos than by her biological father.
But then in Endgame when Clint and Nat go to Vormir he calls her "daughter of Ivan" even though she never even knew her biological father's name and would have thus spent more time with Alexei growing up (albeit still not much time, but at least she remembers him).
Why so inconsistent?
Commentaires
He's asking why she was called "daughter of thanos" when that's not her true biological father.
"DISAPPOINTED!"

the universe basically told him 'no you are not worthy and now you are cursed to forever explain why others are not worthy.'
“It was real to me”
Plus Dreykov do see all of the Widows and even some of his soldiers as his "Children", it could easily be similar to Gamora's Situation that Thanos took over as the "Main" Parent over Gamora's Mom.
I hope we get to see Cap returning the Soul Stone and running into this guy again.
But as the user above me points out, that’s line is enough
I feel like in that context, it's wild anyone would ask how he knew. I though it was kind of obvious.
That being said, one can infer that the Soulstone gave insight to Red Skull so that the names he listed would prove the truth and gravity of his words for someone like Clint for example, who didn't know if he could trust him.
ONE MILLION PERCENT!

I don't need to know the details.
Also this is another reason why I don't think Ivan is Natasha's Biological Father, it's doesn't make any logical sense that Nat would choose Mr. Romanoff over Mrs. Romanoff when she knows in 2023 that Mrs. Romanoff was the one that really loved her and went after her.
It is only his body being used by some magic.
Avengers Doomsday: "How Steve Rogers make babby?"
It's not that deep.
Nat considered herself fatherless in an emotional sense so Skull went with her bio dad
I kinda wish we saw that....
Go a little deeper, and it could refer to not knowing who her father is, as Ivan can be used as the Russian version of John doe (Ivan ivanovich)
Or it could just be something that was needed to convince Natasha that this scenario is legitimate.