Reverend Parris is the minister in Salem. Miller notes, "In history he cut a villainous path, and there is very little good to be said for him." He appreciates and takes pride and comfort in his position of religious authority. In fact, he is more concerned with his position than he is with looking out for the spiritual and ethical welfare of others. He is quick to judge others and is eager to jump on the bandwagon of the witch hunt.
Betty Parris is the Reverend's daughter. We don't know if her illness is real or an act. But in either case, she is somehow affected by her experience in the woods with the other girls. At the end of Act 2, she rises out of bed and makes accusations. This suggests that she is very impressionable. Either she believes that the other accusations (from Abby) are true or she simply wants to go along with Abby's story out of solidarity.
Abigail (Abby) is Parris's niece. Abby's parents had been brutally killed and she does not receive any significant parental affection from Reverend Parris. Abby is attractive, flirtatious, and manipulative. However, her behavior is not entirely her fault. Having received no parental affection, she seeks romantic affection from John Proctor. He obliges but then turns her away. In this sense, the other girls are the only ones who support and stand by her. This doesn't excuse her behavior, but it shows how someone like her might feel neglected.