Help with mysterious behavior of cnc shield and steppers

Hello everyone!

Recently as a challenge to myself I have been building a eye mechanism for a very small animatronic.
There is not much space in the head and because each eye needs 4 motors, therefore I decided to go with very small linear steppers (10mm stroke). I have connected them all to the arduino using a CNC shield and some A4988 drivers. The motors work fine when connecting them individually to the CNC shield. But as soon as I connect both, Just one rotates (if i disconnect the one rotating the other one rotates) It almost seems like one motor is impeding the movement of the other one, i have checked and switched the A, B coils but that has not had any effect. Any Ideas what could be happening?

(Each motor is connected to its own A4988 driver)
(The Shield motor voltage is being supplied by the arduino 5v pin, since the motors are tiny)

Even if the motors are tiny you cannot supply them from the arduino 5V. The A4988 needs a motor supply voltage of at least 8V to operate correctly. And what are the electrical specifications of your motors? May be the A4988 is not a suitable driver for them.
The supply voltage of the A4988 must be significantly higher than the rated voltage of the motor coils. And the current at the A4988 must be set to the rated current of the steppers.

Let's see a good schematic.

Well, I get that! it was a risk that i knew from the start, however I cant wrap my head around why they work individually and not together. The steppers have no specifications apart from being Bipolar, i got them very cheap from china and i cant get any information about them. I was thinking perhaps it has something to do with the capacitor? I have also tried using an external power supply but they dont even turn when i do that. I have also increased the voltage to 8 volts but nothing seems to happen that way either.

Which capacitor?
As @LarryD already wrote, show a good schematic of your setup.

Well, this is how it is all connected. Not much! hahha the stepper motors are correctly wired also, so i did not show every lead in the sketch.

It's printed 12 -36V on the board, lower left corner. Why do You think there is such a printing?

BTW I note your wiring is all loopy all over the place. This is very bad news for interference. All the wires for one motor should be twisted together into one bundle so they don't act as magnetic loop antenna!