Maybe their extended family - Bennets, Bingleys, Hursts - will help them in the next few days wroth the big picture. After all, they reached a preliminary decision in minutes after getting engaged. It is natural that their minds were more busy with celebrating privately their engagement rather than thinking of their children and their mission in life and chances to make a real difference. I would hope that as they get used to the idea of engagement, that they will reconsider. Everyone needs some processing time for major decisions. Surely they will revisit this once the passion of the first minutes of engagement and all soppy "I will sacrifice my identity for you" - "oh, oh, no! I will sacrifice mine for you" passes.
