Searching for Juul Knutsen's parents and siblings

My grandfather, Juul Hagbart Knutsen, a plumber by trade, was either born in March 1877 in Halden or March 1879 in Kristiania. He married my grandmother, Gunda Johanne Bjorkman and they settled eventually in Kristiania. They had many children: Lillian, my mother, Randi, Mary, Gunvor, Aase, Sverre, Eugen, Georg. I have not been able to find out who his parents and siblings are. It's a possibility that his father may have gone by the name of Knute Olsen. I am nearing the end of my research on my family and am missing this information. Thanks to anyone who can help me.