slaughtered Zedekiah's sons before his own eyes

The eyes are a synecdoche for the whole person. The reader should also understand that others probably helped the king of Babylon kill Zedekiah's sons. Alternate translation: "forced Zedekiah to watch as the king of Babylon slaughtered Zedekiah's sons" (See: rc://en/ta/man/translate/figs-synecdoche)