Hi Kathryn
You will need the name of the Department and the village he was born in. If you have this, each Department has its own archives. See
http://memorhom.site.voila.fr/index.htm for links to Departmental archives. Probably the best place to start once you have that info is the "tables decennales" - ten year tables in alphabetic order for birth deaths and marriages for each village. Also there are "recensements" - census for each village that will show who was living in the same house and their relationships - parents, children, servants etc and occupations. This may answer your questions about siblings and what they were doing in France.
Good luck
Lee Hill
en Australie