I could not find Halvor & Anette in 1900 census.I don’t find any other children for Halvor & Anette, but perhaps they had siblings who did.Finding church records in Oslo is a daunting task – unless you know the name of the church and year, you could easily scan hundreds of pages before you find something.
I found a record that Sigurd did marry before Gunvor, to Josefine Elevine Marie Iversen on 7 Dec 1898.But I could not find this record in the scanned churchbooks.He was married when he emigrated, but it seems he did not take his wife with him.She must have died in Norway, sometime after he left.
Sigurd married Gunvor in Manhattan, 3 April 1910 (cert# 7598).
Gunvor left Oslo 3 Jun 1904.She arrived in Boston on 20 Jun 1904.She was going to her brother, O. Hovind in NY.
This is the best match I could find for the birth/baptism of Gunvor (Gunnor), born 5 Jul 1881 at Høstbjør østre (farm), Furnes, Hedmark.Later, her parents (Mathias Simensen and Syverine Olsdatter), moved to Håve østre farm in the same district (which explains her surname). No. 31 on the page. http://www.arkivverket.no/URN:kb_read?idx_kildeid=6004&idx_id=6004&uid=ny&idx_side=-22http://www.arkivverket.no/URN:kb_read?idx_kildeid=6004&idx_id=6004&uid=ny&idx_side=-22
If you don’t already have all this... hopefully, it will get you started.