In The Adventures of Huckleberry Finn in Chapter 22, how does Twain give us a sense of hope for the con men?

I have changed your question slightly to make more sense
as it was somewhat confused. The main action of Chapter 22 isn't actually focussed on
the Duke and the King, but on the mob that has come to lynch Colonel Sherburn and how he
faces them down, and then the trip Huck takes to the circus. Finally we return to the
Duke and the King and their latest exploit as they finally get to deliver their
Shakespeare play. However, this is not a success to put it
mildly:

Well,
that night we had our show; but there warn't only about twelve people there - just
enough to pay expenses. And they laughed all the time, and that made the duke mad; and
everybody left, anyway, before the show was over, but one boy which was
asleep.

It is clear that
performing Shakespeare is not going to get the kind of income that the Duke and King
want, so they decide to have a "low comedy", advertised with the final bottom line that
is actually written in the biggest text, which says:

readability="5">

LADIES AND CHILDREN NOT
ADMITTED.

As the Duke says at
the end:

"If
that line don't fetch them, I don't know
Arkansaw!"

Thus Twain offers
hope to the con men by showing how they have learnt from their attempt to perform
Shakespeare and are now planning something that is more to their audience's level - and
so the stage is set for the Royal Nonesuch, that turns out to be far more lucrative for
the con men.