The word "they" refers to "Edom" and "Egypt" and is a metonym for the people of Egypt and Edom. The words "innocent blood" are a metonym for innocent people whom they have killed. Alternate translation: "because the people of Egypt and the people of Edom killed innocent people in the land of the people of Judah" (See: [[rc://en/ta/man/jit/figs-metonymy]])