"All are punished" would mean (In Romeo and Juliet's time) that all members of the 2 families which are Montague and Capulet would be punished because they displayed that they couldn't be trusted with the other house (Montague with Capulet and Capulet with Montague).
It basically means everyone that's connected to the Montague/Capulet house would be punished for their crimes (the grudge they held towards each other).