I love this! I have wanted for a long time to know how Hestia and Daedalus got on with Vernon, Petunia and Dudley, and this is just about like I had imagined it would be (but even better :-D). You made all of these people breathe and grow beyond the glimpses we get of them in canon.
Hestia deserves an Order of Merlin, First Class for putting up with the Dursleys - I think I would have kept them Petrified if I'd been her. I love her feistiness and her clear-eyed, wry assessment of the people she's stranded with.
And how cute is the crush Dudley, I mean Dudlus, had on "Dave"? That's not one I would have seen coming!
I can fully understand Hestia's anger at Dung, and it's great how you move us so plausibly through their reconciliation and I was glad at Dung's unexpected bit of bravery in front of the Snatchers. He rings true and yet there's lot more to him than we are expecting, and I understand his reaction at Hestia's forward behavior. He's at least half in love, and it's not her he's protecting so much as himself, which also rings true. It would mean something to him, and it would hurt too much to know that it was just a casual one-off to her. So, it's an unexpected pleasure to discover that she picks up on that and decides to court HIM to make up for it. Well done, indeed, Mystery Author!