Hello, My name is Robin (Douglas) Shaw, and I have quite a bit of info on these families. I'm related to them all, several ways. There were two large french communities in Cheboygan Co.. The Cheboygan French, and the Black River French. (this is the way my family spoke of them). The Douglas' were Cheboygan French, the Sova' and the St. Peters were Black River French. Black river is over in Alverno Cheboygan Co..
Austin St. Peter (1906-1972) was the first child of Edward St. Peter (1878-1913), and Felicity Douglas (1886-1969). Felicity's father was Augustin Dugas (1808-1888), but was called Austin. (Austin was my 3rd gr grandfather) I suspect Felicity named her son after her father. Edward St Peter died in 1913, and Felicity married John J. Sova (1873-1960) in 1918. I haven't heard of an adoption for your grandfather Austin.
Interesting note: When all these families left Canada to come to Michigan the names changed. In Canada Sova (pronounced so-vee) was Sauve. St. Peter was St. Pierre. Americanized I believe. Douglas in Canada was Dugas (pronounced doo-gaw) I believe Austin couldn't spell it as it was written down Douglas, the first time I saw it, on his Homestead papers. It is also spelled both ways in the St Charles Church records, but only for Austin. All of his descendents are known as Douglas. This could help in your search.
Note also John J Sova died in 1960 not 1969. You can contact me thru my email
robinmtplsnt@aol.com