Wire length won't make much difference until your clock rates get up to the gigahertz speeds - about a million times faster than you'll find on any CNC machine.

So don't worry about that.

Worry instead that any driver worth two pinches of goat sh1t will attempt to manage current to the motor and that, unless the steppers are IDENTICAL (ie never gonna happen) then one stepper will always be shunting more of the oomph and fighting the other. At best your torque out, already limited by using steppers, is going to be even further limited. At worst, overloading the drivers or one of the steppers and you'll have smoke and sadness and regret.

Best approach is one stepper per driver, pair up the inputs to the drivers instead (if you can't run them independently from your controller and have the software slave them out).