I would not go by that: Author Austen sometimes plays loose and free with group-verbiage. Witness Mr. Collins letter's response, Ch. 13:

To Catherine and Lydia, neither the letter nor its writer were in any degree interesting. [...] As for their mother, Mr. Collins's letter had done away much of her ill-will, and she was preparing to see him with a degree of composure which astonished her husband and daughters.

So, Catherine and Lydia had no interest in anything pertaining to Mr. Collins, and Mrs. Bennett's daughters are astonished at her composure. I take that to mean that, if the two youngest noticed it out loud at all, it was as a joke that Mamma would be okay with 'that odious man' visiting. Likewise, the Lucas boys [being] relieved from their apprehension of Charlotte's dying an old maid, might simply mean that it was noticed as an advantage, not that they all actually felt any great outpouring of emotion at the news.