It's only by chance I came upon your message while browsing the board because I sure did not receive any alert that someone replied to this thread! Weird, I used to before?
No matter, I'm glad to hear from you! Still looking for the Coutard family then? I've checked the records you indicated and you're right, the name is HAVOUÉ and it seems the brother and sister died mere hours from each other! I concur with you too that she perhaps died from learning the news as they both died in their own home, unless they were both ill (unlikely) or wounded together in some accident and brought back home (also unlikely, they would have been sent to the hospital if it was that serious). So... the shock of grief?
Ferdinand's home was rue Trézel No. 8, the street name was changed in 1927 and became 'rue du Docteur-Heulin' in honour of said doctor: http://fr.wikipedia.org/wiki/Rue_du_Docteur-Heulin
Have you managed to find the COUTARD/MAWLE marriage?