I have no answer for difficult handwriting - especially probate records. Church records are usually easier to figure out because of the much more limited usual vocabulary found in them.
You have no guarantee that Peder and Anne's parents have any long term relationship with the farms already found. They might have also only been cotters and moved from residence to residence during their lives. The spelling variations found in the 1801 census are not at all surprising - my general rule is "if it would sound the same - it probably is the same".
To learn history of where and when church records were I always turn first to the LDS Family History Library catalog online. (familysearch.org) In their notes for church records of "Nord-Fron" they say "Kirkebøker, 1816-1914...Contains parish registers for the parishes Sødorp (Søthorp), Kvam and Kvikne with Skåbu chapel. They were separated from the combined Fron clerical district in 1850. For earlier records see Sør-Fron clerical district." So check Sør-Fron first.
You should also check into whether or not there are published bygdebøker for Vågå, and the Fron areas. Persons who specialize in the Oppland area (see the Oppland message board in the Counties folder) might know about them.http://homepages.rootsweb.ancestry.com/~norway/bygdebok.html