Looking for grandfather's half-sisters

After giving up my grandfather as a foster child, my great-grandfather Karl Olai Mikkelsen married and had 5 daughters before drowning in the Alverstraumen in 1881. In the 1900 census for 1257 Alversund in Hordaland, his widow Anna Jensdtr and 3 of the 4 surviving daughters were operating the family farm, Alver. In the 1910 census, they are gone - someone from Bergen owns the farm. Where did they go? I have found no record after 1900. Daughters were: Ingeborg Gurine, born 1868; Andrine Maria, b. 1870; Magreta, b. 1873; Olgaard, b. 1875 (died at 8 days) and Gjetta, b. 1879. Their surnames variously written as Olaisdtr or Karlsdtr. Seems like some trace should remain among these women .