Dan wanted [Grace] to say something special to them: Dan and Amy, I'll miss you most of all. Nobody else in this room really matters to me. (2.107)
Dan never verbalizes it, but he's very hurt that Grace, his grandmother, never did more to help him and Amy out. She never even expressed that they were her favorites. And now she's telling them from beyond the grave? Yeah, that's gonna call for some therapy. After the hunt, of course.
How could Grace have been planning something this huge and not have warned them in advance? (3.23)
Like Dan, Amy also feels betrayed by Grace for not knowing about the hunt ahead of time. But this is a betrayal they manage to get over pretty quickly, once the hunt is underway.
For reasons [Grace] never explained, she'd pressured Beatrice into being [Amy and Dan's] guardian instead. (3.15)
Ugh, a double-dose of betrayal. Not only did Grace not take Amy and Dan in, but she sold them out to one of the most duplicitous guardians we've ever seen. Sheesh. It makes you wonder why they even bothered going to her funeral.
"That must be terrible—thinking you were Grace's favorites and then being left in the dark like that." (3.33)
Ouch. Ian Kabra's harsh remark gets to the core of why Dan and Amy feel betrayed by Grace. It stings, and this is like rubbing salt in the wound.
"I will disown you and leave you to Social Services." (3.51)
As if one betrayal wasn't enough, Amy and Dan also have to deal with Aunt Beatrice saying she'll get rid of the kids for not giving her their inheritance. This betrayal cements the fact that Amy and Dan are totally alone in the world. They have no adults to trust.
"Until the end, surely we can collaborate?" (3.87)
If they had listened to Uncle Alistair's question here a little more closely, Amy and Dan would have noticed the "end" part of it. Who's to decide when to end their little alliance? It's Alistair, who betrays the siblings when it's in his best interest. We're thinking they should have seen that coming, but hey, hindsight's 20/20, right?
[Amy] and Dan crawled through the library, desperately looking for another exit. She had no idea where Uncle Alistair had disappeared. (5.86)
Just to play devil's advocate, let's say Uncle Alistair really was injured somewhere during the fire. Amy and Dan don't even bother looking for him; they just leave. That's not just a betrayal. That could be a fatal betrayal.
Alistair Oh had tricked them. He'd stolen the Poor Richard's Almanack with their mother's notes—their only lead in the quest. (5.122)
And here's betrayal number three. Why do they keep trusting him?
If [Grace] really loved them, she wouldn't have left them in the dark. (15.110)
Even a few days into the adventure, Amy and Dan still feel betrayed by Grace. This reminds us that they are still kids. At 11 and 14, they're more sensitive than the adults are. They weren't given special treatment either.
Uncle Alistair smiled down at them. He looked like a raccoon with his two black eyes. (18.32)
Raccoons aren't exactly the trustworthiest animals. They're little thieves who steal your garbage. That's a good way to characterize Uncle Alistair, who, in case you haven't noticed yet, will betray anyone at the drop of a trashcan lid.