Good story. I always enjoyed the multi-verse stories. As many stories as I have read over the years in the HP genre, I think I have read just about everyone you mentioned. Though magical knife wielding mermen hasn't come up.
Caught your nod to "The Odd Couple". I could imagine Harry and Ron as being like Felix and Oscar after Hogwarts. Though I see Hermione growing up like Elaine (Julia Louis-Dreyfus) from "Seinfeld".