Can I Use Two Different Cables Instead of Single Cable?

If you've got a factory unit, then you've got fire and business loss indemnity insurance. Your insurance provider may want to know why you're going to an anonymous internet engineering forum instead of consulting a local Electrical Engineer directly, Mildred, with all the indemnity involved that your insurance company might expect.

Your local regulations may require all paralleled cables to be the same size.

BS7671 allows parallel conductors of the same CSA with no derating. A 120mm² and a 70mm² is a NoNo. You could use 3 off 70mm²

I usually go 200% load, wire gage for a significant safety factor. DO NOT cut corners or try to cheap out on an application.

Consult with a a local licensed(?) electrician or electrical engineer. They will know which codes pertain to your location. We do not know at all where this transformer resides. Those of us who have the authority to give this type of advice get paid for this service.

what about the fault current?

You have to rate your cable not only for the load but the fault current too!

Technically, however, two smaller cables will have a (slightly?) higher current carrying capacity*, due to larger surface area from which heat can be radiated / conducted / convected -

(*Than a larger cable of the same total cross section)