This was a really compelling story! I read it all day today, and while it contains lots of things I don't usually like, I was glued to the screen until I finished it. The details are in the rec to follow, but I thought I'd mention what bothered me:
Scorpius sighed. "How many times am I going to have to tell you that I do not find it 'creepy' or 'evil' or even 'weird' that you're a Parselmouth? Your father's one, you know. It's not unheard of for it to run in families." -- there's nothing in the books to say that the Parseltongue ability is hereditary. We know that Harry got it from Voldemort because a bit of V's soul was lodged in him, in the Horcrux in his scar. So it's likely that the ability is lost with the removal of the Horcrux. I thought that this moment could have been clarified in the story.
And the second one, concerning the House Stone: would Snape have been wearing it if he was Headmaster, not a Head of house, when he died? Because I seem to remember that Horace Slughorn was the head then. At least it's implied when Minerva speaks to him before the Battle of Hogwarts. If you meant that Snape didn't pass the stone to Slughorn, it could have been mentioned in the story.
But even if they were honest canon errors, I'm not bothered. Because what does it matter when the story kept me reading like an addict?
I loved your portrayal of Godric and Salazar. I loved how you wrote that era at all. I don't usually like Founderfics 'cos they are never written they way I want them :) But your story is exactly what I like: you tell the story of their relationship with lots of fascinating historical and magical details, and I loved it.
Scorpius and Albus were really moving. I was worried they would get locked in the depths of the castle! And Snape/Harry plot was really creative. Well, I'm shutting up :) Thank you very much!