Sir James gets over his bitterness pretty quickly, and soon learns to look at Dorothea with pity, rather than with anger.
He knows that Mr. Brooke won't do anything to stop Dorothea from marrying Mr. Casaubon, so he goes to Mr. Cadwallader, the vicar, to ask him to step in and say something.
Mr. Cadwallader is too easy-going, though. He says there's no reason for Dorothea not to marry Casaubon, so long as she likes him.
Mr. Cadwallader goes on to defend Mr. Casaubon, telling Sir James about how Mr. Casaubon took care of his poor cousins. Apparently Mr. Casaubon's aunt married a poor Polish man and was disowned by her family. That's why Mr. Casaubon is so rich: his mother inherited her sister's share of the fortune as well as her own. But Mr. Casaubon went looking for his poor Polish cousins and gave them money.
Sir James is impressed by Mr. Casaubon's generosity to his cousins, but still doesn't think that Dorothea should marry him.
Mr. Cadwallader is (understandably) convinced that Sir James only cares because he wants to marry her himself, but he denies this. He claims his interest is brotherly at this point.
Mrs. Cadwallader comes in, and sides with Sir James. She thinks her husband should try to persuade Mr. Brooke to postpone the marriage of his niece until she's older.
Mr. Cadwallader doesn't think it's his business to interfere.
Despite the fact that Dorothea's marrying someone else, Sir James still plans to go through with the plans to improve the cottages of the tenants on his own estate according to Dorothea's plan, which pleases her a lot.