To clarify, the Gshield limits the current no matter how many steppers are paralleled. So two in parallel does not double the current, instead it splits it between the stepper motors.
The stepper motor cannot take any more current than what the Gshield is set to supply. It is a chopper drive, which means it is a switch mode current regulator, using the stepper motor winding as the inductance.
I would also strongly suggest you run the motors at no more than 80% of their maximum rated current. The maximum is just that – a maximum. You’ll likely need to place fans on them to run them at 100% of their maximum rated current. An overheated stepper motor can partially demagnetize and then become very weak.
