Thanks for your reply. I subsequently found out that Alexander did die because there was a burial record at St. John the Baptist Church in Edgard. I can't remember the French term used for the cause of death because it seems to have been a colloquialism. There is no exact translation but it implied that the death was kind of "fishy."
I believe my grandmother added the "e" to Legaux. I think to distinguish the family from the African-American relatives.