I talked with my grandfather last weekend about this. He doesn't know why Ole (oldest) took Ambroson while Carl and Peter (younger brothers) took Amberson. They all used Drengmandson until they left the farm. Unless, as someone suggested, they have different mothers.
Apparently, both Ambrose and Anna died of stomach cancer, about three years apart. I have some records that indicate this. However, according to my grandfather, they both died at a hospital in LaCross, WI. However, I have been unable to find death certificates in the state of Wisconsin.
There was one daughter that died around 8 years old and is buried in a cemetery just south of Rushford, MN. I have searched that cemetery and others nearby for Ambrose and/or Anna. However, I cannot find any markers for them. I wonder if they had enough money to buy markers. He was only in the US about 8 years.
Ambrose was a tailor in Norway and why he tried his hand in farming, I don't know. The farmsite near Rushford is atop a plateau. It would be a hike down the hill to fetch water for livestock.
As mentioned, Ole eventually settled south of Portland, ND, Peter ended up near Mentor, MN and Carl near Fosston, MN. Of the three surviving daughters, one stayed in Rushford, one moved to Max, ND and the other to McIntosh, MN.