The 1801 Norwegian census is available as an online searchable database at the Digitlarkivet website.If "Thorsten" was born in Gran in 1800 I would have expected to find him in Gran for the 1801 census and I can't.(Even allowing for the more expected spellings of that earlier time period -- Torsten, etc.)The parents or any of the children you named should appear in Gran for the 1801census -- why don't they?
The parish records for Gran have been scanned and are available online for your "browsing", also at the Digitlarkivet website.I looked for birth/baptisms ABOUT 1800 and through marriages in Gran ABOUT 1830 and did not notice any entries that match or even come close to the information you have.
If this were MY own family research problem I would return to a point in the family tree that has been located and VERIFIED by primary documentation, then I'd redo the ancestral research step by step.Someone may have taken a wrong turn in their earlier research.
Of course I recommend that you also search those records yourself.
The Digitalarkivet web site has been adding scanned images of the original Norwegian parish church records for anyone with Internet access since November 2005.The parish records are also still available for use on LDS microfilm through any of their many many Family History Centers.
The Digitalarkivet web site - http://digitalarkivet.uib.no/cgi-win/WebFront.exe?slag=vis&tekst=meldingarhttp://digitalarkivet.uib.no/cgi-win/WebFront.exe?slag=vis&tekst=meldingar An English option is available by clicking on that word from either the left hand column or the blue link bar along the bottom of the homepage. The scanned images are available from the homepage link "Skanna kyrkjebøker" [Norwegian version]/"Digitised parish records" [English version] which is listed along the left hand column and from the blue banner of links along the top section of the homepage. After you've clicked on that link and a new main page has presented on the screen be sure and read the instructions that are available from the Digitalarkivet for navigating the scanned records.The instructions are available in Bokmål (official Norwegian), Nyorsk (Norwegian), Davvisámegiella (Saami), and English. Recommended basic reading are the "Startsiden" [Norwegian version]/"Main page" [English version], "Brukerveiledning" [Norwegian version]/"User's guide" [English version] and "Om tjenesten" [Norwegian version]/"About this service" [English version].
Good information about translating the formats of Norwegian parish church records during various time periods, many of the basic terms used and understanding how to use the information should be studied at this web site - http://homepages.rootsweb.com/~norway/na20.htmlhttp://homepages.rootsweb.com/~norway/na20.html