Huey and Louie's seperate reactions to the Internal Reveal (Huey having an angry outburst, Louie going into a Heroic BSoD) makes sense when you take the Hidden Depths of their personalities into account. It's been established in a previous episode that Huey inherited Donald's Hair-Trigger Temper, and learning that Dewey hid a secret about their mother would be a major Rage Breaking Point for him. While Louie is the most morally-questionable triplet, he's also the most emotionally vulnerable, so learning the truth would understandably hit him like a sack of bricks.
Related to the above, the fact they make no effort or plan to leave the castle grounds despite having so many reasons to may mean that to keep living they have to stay there. Sure it means they can pass on whenever they want, but it also means that until then they are stuck there.
Likewise, Downy's comment to Webby that she's probably just going to throw out treasured family heirlooms of Scrooge's childhood indicate that she doesn't consider them to hold sentimental value. Considering that Scrooge also seems functionally immortal (she doesn't need the memories if she can always make new ones), that might make a degree of sense, but she did lose a daughter (Scrooge's sister/Donald and Della's mother), and family is such an important theme of their visit and the castle in general, it's a little disturbing how willing she is to dispose of heirlooms. She might be joking or trying to shock Webby out of her stupor, but her tone doesn't indicate that. Has she already resigned herself to the fact that she's going to outlive almost everyone she loves?
