Dagobert, I really enjoy your website and it brings back many memories. A group of us American and German cavers visited On-Jemelle and stayed at the barracks/home of Max and Martha DelPierre. I think this in 1976. Max was a very impressive old caver and Martha spoke 5 or 6 languages, I think.
We visited Pere Noel, Puis Aux Lampes, some River cave and a commercial cave where Max was setting some dynamite in a lower level to open some new passage.
I also understood he was very well known as a resistance fighter during WWII. Similar to Max Cosyns in France, perhaps?