In the play School for Scandal, which character lacks honesty?

Take your pick! The play is full of liars, hypocrites, and backbiters. If one had to narrow it down, however, you'd probably have to give the dishonesty prize to the revolting Joseph, the older Surface brother.
This is a man who likes to pretend that he's the epitome of virtue, a man of sentiment. But in actual fact, he's a lying, two-faced hypocrite, a shameless gold-digger who wants to marry Maria for her money. Not only that, but despite his much-vaunted generosity, he has a profound contempt for the poor, preferring to dispense glib platitudes instead of financial support.
If all this weren't bad enough, he's busily trying to seduce Lady Teazle, even though her husband Sir Peter Teazle is such a great admirer of his. But then, Sir Peter doesn't know the real Joseph; he just assumes that he really is as virtuous as he likes to pretend.