Ellefsen

Looking for information on my great grandmother, Jorgine Nilsdatter Ellefsen born in Oiestad (located her in the 1865 census along with my great grandfather, Halvor Ellefsen born in BO and in 1900 census) and my grandfather, Nikolai Ellefsen born in Ostre Moland. I have located him in the 1900 census along with his mother, Jorgine and brother Helmer. Does anyone have information on that area? Also I need information on my Great grandfather, Halvor Ellefsen, born in BO.