The data sheet mentions an enable pin. Did you connect those? If so, to which Arduino pin? This would be the easiest way to switch a scanner on/off, and also to control this in software.
Those scanners are on the same I2C address? Or different address? If the same address the enable pin is the only way to ensure which scanner you're talking to.
Please post link to data sheet. I really need to see the data sheet to understand how these things work.