An important aspect of Chapter 24 is the hypocricy of Mrs. Merriweather. She thinks J Grimes Everett is so wonderful for helping the Mrunas, but bad-mouths Atticus in his own home in front of his sister and daughter. We see Miss Maudie stick up for him here and put Merriweather in her place. We also see (when Atticus comes home briefly) a different side to Aunt Alexandra. So far we haven't liked her. But we see a tender side to her as she feels for all Atticus has gone through. After she, Maudie and Scout learn from Atticus that Tom is dead (shot to death trying to escape), we see Alexandra raise her head up high and enter the room where the ladies are as if nothing was wrong. From this, Scout learns the true meaning of "acting like a lady." (grace under fire is a term that can be used here)
That's a good question. It is possible that they are sincere, and it is also possible that they just want something to talk about. However, it really doesn't matter whether they really feel sorry for the Mrunas or not. What matters is that either way they are being hypocrites. They say that J Grimes Everett is such a good man for helping them, and yet in their own town they are against Atticus helping Tom Robinson because Tom is black.