Do the witches cause things to occur or do they make suggestions about actions which the characters freely choose to follow?
In Macbeth, the witches simply provide information that leads Macbeth to murder.
The witches chant incantations, and they can see into the future. However, when they give Macbeth information, it is not the complete truth, but half truths. In fact, it is not until the end of the play that Macbeth realizes that he has believed their assurances that he will not only be king but be invincible, and that they have really only told him half truths; in the killing of Duncan, the King, Macbeth realizes he has lost his soul (because it is a great sin to kill a king), and that he will not even have the chance to enjoy the position within the kingdom that has become his with the murders he has committed.
The Elizabethans believed that witches could not make people commit evil, but that they could trick human beings into committing crimes, thereby costing them their souls. (This is Hamlet's worry about believing the ghost in Hamlet: is the ghost real or are the powers of darkness trying to win his soul to its doom?)
The witches do NOT cause things to happen in Macbeth. They give Macbeth information that is only half true, and he chooses to believe their predictions and commits the evil deeds. (Things like the earthquake, howling winds, chimneys falling down, the King's horses attacking each other, etc., are not caused by the witches. All of these things are reflections of the disruption of order in the universe because a king has been killed and the wrong person—Macbeth—is on the throne. These strange occurrences will not stop until the rightful heir sits on the throne.)