IIRC, it is clear in the book that Jane and Lizzy spent much time with their Aunt and Uncle Gardiner in London, around or during their adolescent years. If Uncle Gardiner made a good living in trade, then he is not likely an idiot. Also, he married a woman that seem to have a great deal of sense. I think that is clear in the book, and the actresses of the three color adaptions of P&P reveal that quality. Perhaps Aunt Gardiner was preparing herself as a governess, but saw good qualities in a brother who had a few silly sisters, and decided she could fall into worse situations.
"The avalanche has started. It is too late for the pebbles to vote." -Ambassador Kosh Naranek
