I see that Harald Wester's work was to be a preacher when he emigrated. In most cases this means that he stood outside the dominant Lutheran state church in Norway. It is therefore difficult to find a note on the birth of his children. But I found on the oldest girl (Rakel Wilhelma) who was born in Moss!
Source information: Østfold county, Bysoknet in Moss, Parish register (official) nr. II 1 (1878-1886), Dissenters´ birth records 1885, page 173.
Here's parents listed with their patronymic surname. Harald Nicolai Hansen and Martine Olsen. I think that the name of Wester is a constructed surname not related to their origin. This was quite common to do around the year 1900. At the time, it was a transition from patronymicon surnames, to that married couples (families) should have a common surname and a number selected such constructed surnames.
In 1885, Harald worked in a mill. In 1900 he was a businessman and sold machines.
I think I have found baptism note to both Harald and Martine.
Harald Nicolai was born in Oslo and this is likely the note showing he was born August 25, 1858.
Harald Nicolai Taarnvægter Hans Olsen og Hustr: Christiane Hansen. Faddere: Faderen H Olsen,Arb. Ole Nielsen Klokkerdr. Ole Olsen, Moderen Christiane Hansen, Pigen Anne Marie Hansdtr
Father: Hans Olsen worked as «a tower guard». Probably a type of alert service within the fire brigade.
Source information: Oslo county, Trefoldighet, Parish register (official) nr. I 1 (1858-1863), Birth and baptism records 1858, page 21.
Martine Olsen was born in Nykirke parish in Vestfold county. She seems to have been born out of wedlock, December 24, 1863.
The mother was unmarried woman Anne Olea Olsdatter from the farm Kopstad, in Nykirke parish, Borre municipality in Vestfold county. Her father was unmarried man, Mathias Olsen lives on the farm Haug, but born in a neighboring parish. He came from the place Grette, Våle parish and Re municipality in Vestfold county.
Source information: Vestfold county, Nykirke in Borre, Parish register copy nr. II 1 (1842-1877), Birth and baptism records 1864, page 56-57. Permanent pagelink: http://www.arkivverket.no/URN:kb_read?idx_kildeid=8170&idx_id=8170&uid=ny&idx_side=-30