Sorensen of Horten, Vestfold and Oslo

Hi, I am searching for any descendants of the Sorensen family of Horten, Vestfold. I have seen the census entries up to 1875, they were at an address Carljohansvaern. The father's name was Bergerius Sorensen, born circa 1808 in Porsgrund. He went to England in the 1830s and returned there to marry my cousin Harriet Davis at the Old Church, St Pancras in 1846. They had two children Harald born June 27, 1847 and Hilda Louise born November 5, 1856. I can not find any record of the deaths of Bergerius and Harriet Sorensen, though I have searched the parochial registers for Horten between 1875 and 1900. I could be missing something. And the script is very hard to read at time, as I don't understand Norwegian. I know that Harriet, Bergerius and Harald were all dead by 1900 as they don't appear in the census. The only surviving members of the family were Elisa Sorensen, Harald's widow and their only child Ragnhild, born February 28, 1877. They lived in Oslo. Does anyone know how I might find the death records of this family and also find any descendants of Ragnhild, who I assume lived to have a family of her own. Thanks, Daniel