The characters are all linked together by the accusations of a group of young girls who were afraid of being punished for dancing in the forest. Because of mass hysteria, even those who did not believe in the accusations of witchcraft, like John Proctor and Rebecca Nurse, end up losing their lives because they will not confess to something they did not do. Ironically, every character is caught up in a web of accusation or the consequences of those accusations and the tragedy is that no one dared stop the injustice until it was too late for 19 men and women. Whether they wanted to or not, the characters all belonged to a community more absorbed with finding witches than finding the truth.
Another topic you could explore related to belonging is how the girls keep the accusations up because of all the attention they are getting. Remember, that in the Puritan society, children were to be seen and not heard. In the intro to the play, Miller writes that Reverend Parris thought of children as "anything but thankful for being permitted to walk straight, eyes slightly lowered, arms at the sides, and mouths shut until bidden to speak."
Because the children lived in such a strict society, remember even dancing is an extreme offense, where they were basically to be seen and not heard, when the girls begin accusing people, they learn that they now are the centers of attention. They wield a considerable amount of power. People gape at awe at the girls.
Look at how the crowds part for Abigail when she walks down the street. Look also at how important Marry Warren has suddenly become. Instead of just the proctor's servant, she now is a deputy of the court and has power over those who once had power over her.
Now the girls belong to a group, the accusers, and their power is addicting. The more people they accuse, the more power they wield and the longer the trials will last.