Wow, what an extraordinary and unexpected story. Just recently I was having a conversation about how we hadn't seen a really good look at autism in the wizarding world - and here it is! I think Cuthbert's voice is very solid and believable here, and fits right into what we know of him from the books.
I love how you didn't whitewash Walburga's bigotry, but still showed her to be a three-dimensional person one can sympathize with. You can tell she's on the verge of seeing the injustice of the world she lives in, but doesn't quite have the courage to face it, and be shunned by everyone she knows, just another name burnt off the family tree.
And Filius's cameo is a real treat - his practical approach is very Ravenclaw and very him.