I am not related to the family. I just enjoy helping people with their Norwegian research.
The birth date listed for Julie says "19/767" which would be "19 July 1867". This is obviously not correct - the way it is entered there is no way to tell what was meant. There seem to be several years of missing records in Biri. The births for 1876 are not listed, so I can't check the original records to see the correct date of birth.
You are correct about Gudbrand using the name "Gustav".