You are absolutely right about the lack of people to care about at the start of MP. Reminds me of the beginning of Emma! JA is asking a lot of her readers to forebear with the opening chapters of MP. And, your reaction to the Crawfords is exactly the reaction I think JA sought. They are lively, funny, witty: They seek to disturb the deadly, dutiful order of MP.

I am reminded of Richard the III by Shakespeare where no one who is supposedly "better" than the evil king has any spark or strength of character. In contrast, the evil Richard appeals to the audience in the theater, and you want him to escape at the end when he cries "A horse, a horse, my kingdom for a horse." Shakespeare manipulates his audience to cheer for the bad guy, and we also cheer for the Crawfords, even though we suspect they have suspicious backgrounds. I mean, JA calls their uncle "vicious"! What good could come from that?