You need stepper drivers that can comfortably supply the current required by your motors. A Pololu DRV8825 should be suitable for the 1.8A motor but you would need a driver that could manage 3.5A or 4A for the 2.8A motor. Unfortunately that moves you out of the hobby price range. If you just want to buy a high current driver you will be able to use it with the smaller motor if its output current can be limited to 1.8A
I suggest you Google for 4amp stepper driver. Gecko is the expensive brand. Leadshine is a cheaper brand.
Do not be tempted to buy a simple dual h-bridge that is primarily intended for driving DC motors.
...R
Stepper Motor Basics