Ottum/Lerum Johannes and Martha

Does anyone know where these farms are in Norway (I believe in Sogn).? Lerum might be in Lom. These are my ggrandparents. I'm having trouble finding sources for information I have. According to my old records (recently pulled out after years) I have the following. Johannes Johnson (changed from Johannesen when he came to America I think) My grandfather went by Johnson until the mail got mixed up because there were so many Johnsons, so took the farm name of Ottum. Anyway, Johannes Johannesen was born in Norway on 24 Oct. 1835 in Sogn, Norway He died between 1874 and 1885 in Wisconsin (probably Modena, Buffalo County). It is said he drowned in a beef slough. Johannes and Martha had 7 childern I think. Carrie, Anna, a female, Johanna, Christian, Olaus, and one more boy. (from Sophia Robinson) Martha (Christiansdatter?) Lerum was born in Norway 18 March 1836, also in Sogn according to my notes. She had a second marriage to Andrew Olson (Oleson?) after Johannes died. She died sometime around 1885-1890. I think she was living in Minneiska, Wabasha, MN at that time. I have an 1880 census that shows a Martha Oleson there and one for Andrew Oleson. She was 54 and he was 64 years old. Some of this could possibly be in the Luster County History by Lars Oyane. In a letter from Sophie Quale Robinson, a niece of Olaus Ottum, she said that Martha had a big growth tumor in her abdomen. She also had one son with Andrew that was 11 years old when she died. I will dig further and see if i can find moer in my records. I'd apprciaet any replies. I'd really like to find them in Norway. Thanks. Marsha Owen