Chalmer family in Oslo

Hello, I am trying to find date of birth and death for 3 children of Thomas Chalmer. Thomas Boteler Chalmer b1843 d 1887 emigrated to Oslo from England around 1865. In 1867 he married Augusta Olava Ohlsen in Oslo. I have them on 1875 census with son Thomas jnr b 1871 and daughter Edith b 1875. Their daughter Margaret b 1868 is at her uncles house. 1879 son Vernon was born. They also had 3 other children: Augusta, Florence and Sidney Herbert and would like to have birth /death dates for them if poss and a death date for their mother Augusta, we think after 1916. I can not find them on 1900 census. In 1901 find mother Augusta living with her daughter Margaret. Also found Thomas jnr with his wife in 1901. Thomas senior was a merchant and also had something to do with the church in Norway. Thanks Shirley