Oh, this is lovely. I am in awe of your ability to take two seeming misfits and, not only make them human but also fit them together as though they should always have been joined. I love the structure and the way you used the prologue to support is wonderful
Plus, I love the fact that you took Albus's throw away comment regarding his brother's fondness for goats and turned it into something beautiful. And also something that is reflective of the state of their relationship as brothers.
And this bit of commentary on JKR's Snape backstory...
He left the lad his secrets. It made him more interesting.