Amos taking the initiative to pay for his wife's lawyer. He's not conned into it; he does it without any promise that Roxie has changed.
Roxie is shown being perfectly civil to the Hunyak. Everyone is also genuinely saddened when the latter is executed.
Billy Flynn despite berating Amos for not bringing enough money takes the $2,000 and tells him, "Your devotion to your wife is very touching." While Flynn later does a song and dance around Amos to win Roxie's case, he seems sincere in that moment at least.
Before they enter the courtroom, Roxy confesses to Flynn that she's scared. Flynn smiles and reassuringly tells her, "Don't be."