I have a similar situation - I am looking for 3 Bohart brothers (possibly named Bucheidt/Buchheit. There are a few versions of the family story but the stories agree that the brothers were from Alsace-Lorraine, and that they were in Napoleon's army. One story says that they were part of his bodyguard and escaped before he was sent to Elba. It is believed the family originates in Bavaria. They emigrated to the USA.
I would appreciate new ideas! Has anyone found records that can be searched for names in Napoleon's army?