Torstin

I'm still seeking family history on Torstin Olssøn as his name is written in the 1865 census where he and his wife Mali are living with his parents Ole Gunderssøn and Gaulaa Pedersd. Is there a "Bygdebok" for Hegra that shows the family heritage. Could it be possible that if Gunder #788 is their son that maybe he had a different mother? Gaulaa would have been 46 years old when Torstin was born and 25 years old when Gunder was born which is very possible. I need to "put this to bed" and go on with my history. Many thanks to all for your patience!