I suppose you could use a bus or something to cycle through the cameras one at a time?
Why not use a lower-resolution I2C camera module? I2C allows multiple devices to be connected to the same I2C port, as long as they have different addresses. You can also use one with lower resolution for QR I suspect.
An alternate method would be to buy QR-code recognition modules, with some form of serial output. Then connect all of those to the ESP32, if you can do 5 software serial ports. More expensive this way though.