Help needed locating family of old letters

Hello, Not sure if anyone here can help, but I've been on a mission for a over a year and have been unsuccessful on my own! Here is the story: During WW2, my Mother in Law exchanged letters with a young man who lived in Rennes. I've been trying to track down someone from his family who might want to have these letters. If this man is still living, he'd be in his 90s, so most likely would need to find son/daughter, etc. My problem has been the language barrier, as I speak no French! I was hoping perhaps someone here might be able to suggest someplace in Rennes where I might be able to find out information while working with someone who speaks English! I do have an obituary of someone who might be this man, but have not been able to confirm it. Does anyone here have any ideas?! Thanks in advance!