How we cite our quotes: Act.Scene
Quote #4
Fran… Like mistletoe on sere elms spent by weather,
Let him cleave to her, and both rot together. (2.1)
Brachiano's lustful passion for Vittoria will just lead to death and decay—it's breaking down the social and family order instead of building it up.
Quote #5
Lawyer. What, are you in by the week? So—I will try now whether they
wit be close prisoner—methinks none should sit upon thy sister, but
old whore-masters——Flam. Or cuckolds; for your cuckold is your most terrible tickler of
lechery. Whore-masters would serve; for none are judges at tilting,
but those that have been old tilters. (3.1)
This is more comic relief—"tilting" means having sex. Flamineo is saying that a whore-master (pimp) is better qualified to judge crimes related to lust, since a pimp makes a business out of sex. Also, even though their wives cheat on them, cuckolds are apparently experts on sexual matters, according to Flamineo.
Quote #6
Mont. Oh, your trade instructs your language!
You see, my lords, what goodly fruit she seems;
Yet like those apples travellers report
To grow where Sodom and Gomorrah stood,
I will but touch her, and you straight shall see
She 'll fall to soot and ashes. (3.2)
Even though Vittoria is easy on the eyes, Monticelso claims that she is inwardly corrupt (using the metaphor of the apples of Sodom—a real plant, though they don't actually turn into real ashes: they're just filled with a gross bitter sap). Lust can't distinguish between the way someone looks on the outside and how they look on the inside.