Well, remember, Ron knows that this is Harry, after all, so of course he isn't going to malign his best friend! And Hermione knows too, so they won't be surprised at all when Dumbledore reveals the identity of the Snape look alike.  And Aria is not what you think she is at all, she actually has a very well developed background, she's not phenomonally pretty, except when she smiles, and Snape certainly is not fantasizing about her.  She is not a perfect person by any means.

And I had the Snapes return to Hogwarts because I wanted Harry to meet Sirius and since this is an Au fic, Voldemort might not be restored the wya he was in the books, plus the fact is that Harry wants to prove that he's not the prophecy's pawn by fulfilling it in a different manner . . .with the help of his father, who will fight the final battle BESIDE him and be instrumental in defeating Voldy once an for all.  None of this could have happened unless they returned to britain, and so while it may look like they are fulfilling the old prophecy, they're really sending it down a different fork. 

Wait and see what develops, after all this is only the first chapter!