“every soul.” This is the use of “soul” as an individual. The Hebrew text uses a collective singular, “all the soul” for “every soul.” [For more on “soul” see Appendix 7, “Usages of ‘soul’”].
“There was not one left who breathed.” Joshua was obeying the command of Yahweh in Deuteronomy 20:16-17. This is repeated in Joshua 11:14 for emphasis.
“And he burned Hazor with fire.” Joshua burned only three cities in the conquest of Canaan; Ai, Jericho, and Hazor (Josh. 6:24; 8:28; 11:11). In this last phrase, the pronoun and verb change from plural to singular. Joshua was in charge and he gave the order (cp. Josh. 11:13).