The heroines' marriages in Jane Austen's novels are the antithesis of the conventional marriages in her time. So true, but how can I explain that?
In general it's quite clear and easy to explain. But when it comes to each single novel (NA, S&S, P&P, MP, E, P), I don't know how to prove this matter of fact.
I would compare the marraiges of the heroines to the other married couples in the novels. So in the case of P&P
Conventional couples would be Charlotte and Mr Collins and the Hursts. Their marraiges were prgamatic and motivated by financhial gains or family responsibities
You then have the Bennets who were in love but who were ill matched in temperment, as were Lydia and Wickam who were motivated by lust.
Compare them to Jane and Lizzy's marraiges and you see real affection, without the distraction of financhial insentive (yes they marry welathy men but it isnt their motivation) and a match in temperment, where they compliment their partners personalities.
Going through this process with the novels that you need to cover will give you a decent structure to work from.