In response to Macbeth's second set of prophecies in Act IV, what did the witches do?

The Weird Sisters don't really do anything to respond to the prophecies that Macbeth receives from the apparitions that they conjure in Act IV.  In fact, we never see them again on stage after that second set of prophecies. 

In reference to the apparitions, however, the Sisters do conjure them at the behest of their leader, Hecate.  As she said, "And you all know, security / Is mortals' chiefest enemy" (3.5.32-33).  The witches' plan is to make Macbeth feel secure so that he lets down his guard.  Hecate says that feeling safe is actually our biggest enemy because, when we feel safe, we aren't as alert to danger.  Macbeth will be easier to harm if he feels that he is unlikely to be harmed because he won't be on the lookout for danger.  So, the Weird Sisters conjure apparitions that offer enigmatically worded statements designed to make Macbeth feel safe (but that actually can come true in unexpected ways).