Where? And who are the “they” you are referring to?
Why are two-thirds destroyed in chapter 13 is they repented?
It is my interpretation that after the Nations that come against Israel are destroyed the people of Israel realize and repent. I will concede that I could be wrong on that point but it seems correct from what I have studied.
Zechariah12:10 And I will pour upon the house of David, and upon the inhabitants of Jerusalem, the spirit of grace and of supplications: and they shall look upon me whom they have pierced, and they shall mourn for him, as one mourneth for his only son, and shall be in bitterness for him, as one that is in bitterness for his firstborn. 11 In that day shall there be a great mourning in Jerusalem, as the mourning of Hadadrimmon in the valley of Megiddon. 12 And the land shall mourn, every family apart; the family of the house of David apart, and their wives apart; the family of the house of Nathan apart, and their wives apart; 13 The family of the house of Levi apart, and their wives apart; the family of Shimei apart, and their wives apart; 14 All the families that remain, every family apart, and their wives apart.