Given the subject matter, it will pretty much all be subjective. There are people here who could give you advice on converting a color landscape or other photo to BW in a way that makes it look like it was taken with BW film, but that's not the case here. There's no "right" way to do what you want except the way that gives the results you like. I highly recommend LightRoom if you have it. Click B&W on the HSL/Color/BW tab and use the sliders to change how each of the hues is converted to gray - very flexible!