Yes, in theory it would work. However, the line output of the mixer is not designed to be loaded by four line input devices, let alone speakers. You'd need a headphone amp type device, and by that point you may as well buy an inexpensive intercom power supply and a few beltpacks. Or just get radio's (NOT GMRS/FRS, needs to be either MURS or
licensed UHF business two-way; see my previous thread on the legalities of radio's for
theatre use).