All the Israelites would mourn; this would be a national repentance. The repeated phrases "every family by itself" and "their wives by themselves" solemnize the mourning and underline its genuineness. [source][source][source]
"The wives are spoken of as mourning apart because in public lamentations the custom prevailed of separating into groups, also according to sex." [1][source]
"The closest relationship is as nothing in [2] presence of sin and God as its judge. Each must be alone." [3][source]
This would not be a national media event staged by the leaders of Israel to make a show, but individuals everywhere throughout the nation would sincerely voice their remorse. [source][source][source]
"Individually and corporately, this is the experience of Leviticus 16 (the Day of Atonement) and Psalm 51 (a penitential psalm) on a national scale.... Isaiah 53:1-9 could well be their confession on the great occasion." [4][source]
The houses of David and his son Nathan represent the political branches of the nation, though not just the kings, as reference to Solomon might have suggested (cf. 2 Samuel 5:14). Feinberg believed that this Nathan was the prophet of David"s day, so he represents the prophets in Israel who will repent. [5] This is a minority view. The houses of Levi and his grandson Shimei represent the religious branches of Israel, though not just the main ones that reference to Gershon, Shimei"s father, might have suggested (cf. Numbers 3:17-18; Numbers 3:21). Perhaps the political and priestly families received mention because they were those chiefly responsible for Messiah"s death. When these leading families mourned, all the other citizens would follow their example. The families of Nathan and Shimei may have been the most prominent families of their kind in Zechariah"s day. Zerubbabel came from Nathan"s line ( Luke 3:23-31), and the Shimeites presumably dominated the Levitical classes in the postexilic era. [6][source]
"Nothing can excite to repentance like a view of the crucified Saviour." [7][source]