You best start with improving your schematic and add ferrite beads and capacitors to at least separate the MCU voltage from the motor driver supply voltage.
It of course depends on the stepper motors you are going to use, but with 9 of them stepping at the same time currents might get high enough to have the voltage drop and the MCU to fail.
On the PCB it will also be better to make a separation between two power and ground planes. One set underneath the motors and one set underneath the logic. Connect the two via ferrite beads.
Also depending on the amount of current the stepper motors need I would use a switching power supply (buck converter) to at least make the motor supply. Will improve on the power loss over the PCB connecting wires and also less heat generation on the PCB.
Then the AH3572, which seems to be
not recommended for new design is an open drain device and needs a pullup resistor to work. In your schematic you draw in a pulldown resistor of 1K. I don't think internal pullups in the ATMEGA2560 will be able to get the level up to high.
So best head back to the drawing board and read the datasheets and look into currents needed to let it work properly.