It was not acceptable to free a slave.  Tom doesn't feel the same way about Jim that Huck does. Huck has a closer relationship to Jim, so it is more acceptable for him to break a law to free Jim.  Tom thinks that it is wrong to free a slave, even though he helps Huck to free Jim.
Twain attacks the white attitude of thinking that they are above everyone else in Huck's conversation with Aunt Sally.  Aunt Sally is thankful when she thinks that a black man was the only one killed. This reinforces the theme of
Twain uses this skill while Huck is debating what to do about Jim.  Huck isn't sure whether he should turn Jim in.  He thinks that the right thing to do is to turn him in, but he likes Jim.  It is ironic that he thinks that the right thing to do is to condemn Jim to a life of slavery.  Twain is using this irony to attack the racism of the south, and the things that they taught their children.
Huck runs away during the big commotion of people finding $6,000 in the coffin.  Unfortunately he runs into the con men later because they had the same idea of running away that he did.
Huck decides that he doesn't want to turn Jim in.  He is friends with Jim and doesn't care that it isn't socially acceptable, he trusts and cares about Jim.  Huck decides he is going to steal Jim back from the man that is holding Jim captive.
Jim is at the raft.  Twain didn't involve Jim because Jim is a slave, and it would cause problems in the town if they were walking around with a slave.  Also there would be a fight if Jim found out that the con men weren't the king and a duke.  Finally I think there would have been a problem with Jim if he found out that a slave family was being separated because of the con men.  It is
Huck is afraid that Mary Jane, because she is a fragile girl, will betray emotions on her face and give away the plan to the con men.  Huck doesn't want Mary Jane or the other girls to get hurt, and he is afraid of what will happen if the con men find out that they know about their plans.
They Wilks girls are sad because when they sold their slaves, the one family got separated.
It shows how little slaves got to see and know their family.  For a father to not even know that his daughter is deaf is sad.  The slaves barely got to see each other, and families are so often separated that it is not unheard of for children not to get to know their fathers or mothers.  It also showed how much Jim missed his family.
They put on the playbill that women and children are not allowed to attend.  It plays on people's want of the forbidden fruit.  People want what they can't have.  The scandalizing part of it being only for men makes men want to come.  It also shows the sexism of the time by believing it is only appropriate for men.