"with Jehoshaphat leading them." The phrase "in their lead" is an idiom. King Jehoshaphat was in front of the whole army as they went back to Jerusalem. (See: [[rc://en/ta/man/translate/figs-idiom]])
They rejoiced because their enemies had been defeated. AT: "rejoice over their enemies' defeat" or "rejoice because their enemies had been destroyed" (See: [[rc://en/ta/man/translate/figs-explicit]])