Thomas Oleson Beitland (Butlandsbjorgen)

I am researching my husband’s family that immigrated from Norway in 1865. I have found the family listed on the "Bergen" out of Trondheim. They are listed as: Thomas Olsen Butlandsbjorgen, Eli Larsdatter Butlandsbjorgen, Ole Thomasen Butlandsbjorgen, Lorentz Thomasen butlandsbjorgen, Bereth Thomasdatter butlandsbjorgen, Elizabeth Thomasdatter Butlandsbjorgen and Kirstine Thomasdatter Butlandsbjorgen. I have found marriage info for Thomas and Eli and birth info for Ole (my husband's ancestor). I am trying to find Thomas Oleson's parents and birth information. Also, I have a name question, I see that they actually went by Beitland. I know that the third name is their farm or location name so can anyone explain the change? Thanks so much for any help.