how would you turn two on simultaneously
You do not turn on a motor, it is on all the time. You step it, that is you give it a pulse on the step pin or you change the control outputs.
So delay and step and delay. You can skip stepping one of the motors every other time if you want it to run at half the speed of the other.
What software are you using? The stepping motor library is not suited to driving more than one motor.