I would not mind the Duke holding a grudge against the Bennets (well, aunt and uncle Bennet) for some time. Thomas was told by three different people about Wickham and Elizabeth begged him to keep Lydia at home. The duke does bear some responsibility for not "reminding" Uncle Thomas of the importance of propriety, especially as it nears Elizabeth's debut.
It appears that Darcy had a hand in Lydia's "rescue," and even if he did not, it seemed odd that he'd encourage Elizabeth to open letters from home when he'd deduced she was unaware what happened--those letters could only contain that info which would upset her. Why did he come to see her? Will Elizabeth write the truth to Georgiana? Perhaps she'll meet the Darcy/Fitzwilliam clan privately since D and G were asked to come for the little season. I'd hate for Darcy to be blind sighted at a ball!
Caroline, Caroline, Caroline...so she removed Louisa's letters from the post tray, huh? Can someone please "cut" her, please? In some fantastically public manner. Yeah, Louisa and dear, dear, Bingley. spineless as ever, but a dear anyway!