Sanji opposed nami when Zoro stood up for luffy's respect and stood against ussop coming back without atoning for his deeds.. and she tried to justify it by saying "Oh that's a formality ehmehm and he's a friend.. "
he also stood by when nami was crying at luffy and ussop were having at eachother..
He also bet luffy infront of her while glaring at her.. so sanji knows reason when it comes down to it even if nami opposes that notion
Yea nami has been inconsiderate when luffy shut her up for blabbering too much.. but she has been the voice of reason whether luffy opposed it or not.. that includes the time when she tried to form a reconciliation between ussop and him by reasoning with him but it was too late..
Another instance of her being the source of realization for luffy is when luffy was stuck between buildings and nami had to expound what robin's doing for their sake.. which helped luffy realize the gravity of the situation..
And Zou she was the the one who supported sanji's retrieval when even Zoro denied.. you could say sanji was just that important but you can't deny nami gave luffy that push against what zoro said..