What controller does it use.? If it's a parallel port then mach3 will let you use slaving. If it's USB or Ethernet then it's an external controller and that will determine if can or cannot use slaving.

Whether you can use 2 drives from one Output will depend on the current of the Output and what the drives will draw. It can be done if you have the current.

The downside, other than putting extra stress on the Output, is while it allows you to drive 2 motors they can't be controlled individually so the gantry cannot be squared using Home switches at each side.

Don't run 2 steppers from one drive. this is a very bad idea that will make the motors run very rough.