Working on your phone - yes, that's hard, to see all the information posted.
The Olsen / Larsen difference is normal to Norwegian genealogy. You have an Olsen / Larsen split in a family of siblings, in your notes, and the family thoraway found has the same split.
Norwegian names, as you know, were based on the father's first name +son or +datter.
Son of Lars would be Larsen; daughter of Lars would be Larsdatter.
As times modernized, so too did Norwegian names.
Lars Olsen would have children named Olsen in modern times - just as in the USA.
The children of Lars Olsen in Norway show the shift, as oldest children are using "Larsen" and youngest children are using "Olsen." At least that's what it looks like, from the little information and few records found to date.
I'm not saying it's the wrong family - just that it's possible it's the wrong family and we should nail it down.