Searching 3 G-aunts who stayed in Norway

I am searching for the names of my grandfather's three sisters. The family is from Arendal, Norway. The parents were Ole Emil Berntsen (b. 1855) and Johanna Olsen Berntsen (b. 1858). They had six children. The parents and their three boys, Aksel (1878), Bernt (1889) and Christian (1895), all emigrated to N.J., USA. I am trying to learn about their three sisters (one of whom may be Fredericka) who stayed behind in Norway. Any suggestions how to go about searching are much appreciated.