There is not as much to say about the other two items since there is no documentation identifying the occasions or persons in the photo. No caption is needed in the first one. That is President Charles de Gaulle shaking hands with Arnaud. The great war hero and political leader was the president of France from 1959-1969. He died in November of 1970, so that could date this photo to sometime in the later 1960s, possibly after Arnaud had inherited his father's estate in 1968.
That is a United States military uniform on the right and there are four stars on each shoulder. I have looked at a list with photos of U.S. Army four-star generals stationed in Europe during the 60s and 70s but have not been able to identify him. Could be another service branch. I have no clues about the man in the middle. I considered maybe American ambassador to France, but that face doesn't fit any office incumbents (Sargent Shriver was one) in the right time frame.
Two possible theories. It could have something to do with Arnauld's involvement in the veterans organization in Paris. Or it could have something to do with the 1973 peace talks that we know were conducted in Arnaud's house. Notice that there is some kind of electrical controller on the table in front of them, and some kind of an easel display (possibly a map) behind them.