I can understand why you feel hesitant to contact people out of the blue and if dealing with a foreign language, then you should consider using a "native" speaker.
Might I suggest that Mark 727 ask his mother to make contact on behalf of Brian? That way you both have a connection, a "native" speaker makes the initial contact (and with a personal reason in a similar case may be easier to establish a rapport).
I can't see any good reason to delay, 65 years have past, how many more? Witnesses aren't going to be around for many more years whilst you debate how to make first contact.
Mark 727 Mum is hardly going to be totally insensitive, in fact she probably will be more understanding, knowing how crew relatives feel.
Do please, try, and soon. Once you have helped Brian, it may help with making the first contact in your own case.
As to the crash site, I can only say that at Arnhem, the crash sites there still show up as burnt patches. There is one next to the lane leading to the D151, but there are also a couple of what appear to be greenish disturbed patches elsewhere, so I can't help there.
Perhaps there is another French speaking Pal on here who might volunteer, or suggest an alternative contact, such as the Mairie or nearest Gendarmerie to establish their credentials as a genuine caller (and perhaps verify the contact details of a younger relative who could "break the ice".
Do you think that these people would NOT want to talk to you?
Please try, they may not want to talk, in which case you have at least tried.
They, too, may have been waiting 65 years for someone to come back and tell them they survived and that their help was appreciated.