This part of the novel concerns one of the Duke and the King's most ambitious scams - the impersonation of the brothers of Peter Wilks so they can seize his inheritance from his daughters, sell the property and take all the money. What is key about this stage of the novel is how it ties in to the overall theme of Huck's coming of age - his growing maturity as an individual and his sense of what is right and wrong plus his determination to act to support what is right.
It is in Chapter 26 where this turning point occurs in Huck's life. He is forced into telling ever more elaborate lies by one of the Wilks sisters, Joanna, about his life in England. As he fears he is going to be doubted and denounced, Mary Jane and Susan rebuke their sister for denouncing and doubting their guest and force her to apologise. This has a major impact on Huck as he is made to see how nice and pleasant the Wilks sisters are:
I says to myself, this is a girl that I'm letting that old reptle rob her of her money!
It is after this episode that Huck determines to do something to prevent the success of the Duke and the King's scam and decides to rob the money. Although at this stage he is unwilling to denounce them openly, at least we are seeing that he is beginning to act on his conscience and defend what he thinks is right.