Ya the number of motors shouldn’t make a difference. The current would be impossible to measure accurately with an ordinary ammeter while the stepper is moving anyway as it would be constantly changing.
As for measuring when the motor is holding, I’m not sure exactly what the driver will be doing at that point but I’m guessing it’s still pulsing the coil at high frequency so that could be throwing off the readings that you’re getting.
What are you using to measure the current? A multimeter in series with one of the coils?