Great pic! Thanks for posting!
One point several members have discussed in the past is the wheel lock ring... in the picture of your great grandfather's car, it shows it as in most original pics I have seen, painted black (or at least the very dark body color, whichever it was), and not chromed.
I wonder what would the Belgian law must have said about side fender lights, as the cars came originally equipped with them, in about the same shape as the headlights. And speaking about headlights, of course I could not swear it, but it appears to me that the lenses in your family's car were changed and the car is using a clear glass, just as with the Marchals of the era. Perhaps it was also a law thing in France or Belgium.
Thanks again!
victor