Two inputs would require two input planes. Both will inject their source respectively but one will be designated as the “Key Input Field” in your simulation settings. This is the input plane that will provide its central wavelength for any calculations that may require it.
The input plane as an object will cover the corresponding cross section of your domain (i.e. a Z-directed input plane will cover the XY cross section). However, you have full control over the center and width of the field it injects.