Augustus is his brother - Noel/Christmas,Augustus,Leon, and Francis (Sr) were the 4 sons of Pierre Arcand. From the stories I hear that Augustus married Rosa Matt and that she may have been Sarah's sister. They always said "2 brothers married 2 sisters"...So that's why you will see a lot of Augustus "Augustin".
Most of the rest I found before, except the baptism - that's another piece of gold. :) I didn't find the baptism before because I didn't have the parents names before (which you've now verified with that Holy Cross record).