How we cite our quotes: All quotations are from You Can't Take it With You.
Quote #4
MRS. KIRBY: She's probably from some dull middle class family; as soon as Tony sees us all together he'll realize how impossible it is.
The joke here is that Alice's family isn't dull at all—and not exactly middle-class either. Also, the family's difference is exactly what attracts Tony to them; he's sick of bankers, and wants to find something a little more exciting (something with harmonicas.)
Quote #5
ALICE: [to the Kirby family] The next time you want to go slumming, stay away from our neighborhood!
Alice is defending her family and their neighbors, who are all gathered in the courtroom. It's the common people vs. the snooty bankers—a sentiment that must have resonated during the Great Depression, when there was (as now) great inequality.