Here's the page showing their entry:
A close-up picture:
Excerpts from the 1873 Marriages for Gustavi Cathedral parish in Födra Dom Deanery for Göteborg Diocese and County. Page 19. ... Number 51. March 30, Westman Johan, sailor and Andersdotter Amanda Mathilda, young lady. Born 1840/1848.
So far, every single record I've seen spells Johan's surname as "Westman."
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Here are the birth records for Johan and Amanda's seven children.
Gustavi Domkyrka, Göteborg. 1873. May 5. Fanny Constantia (...) Illegitimate. Westman Johan Sailor. Andersdotter Amanda Math/a. Mother not married. [Incorrect in record. They were married, but perhaps Johan was off at sea.]
1876. Gustavi Domkirkr, Göteborg. No. 224. February 23. Bertha Maria. Legitimate. Father Westman Johan, Sailor. Mother Mrs Andersdotter Amanda Mathilda. Mother married. Age 35/27.
Gustavi Dom, Göteborg, 1877. No. 42. December 28. Female. Gerda Hildegard. Legitimate. Westman Johan Sailor. Mrs. Andersdotter Anna Mathilda. Mother married. 37/29.
Anders Johan Herbert
1880. Gustavi Domkyrke. No 534. May 16. Male. Anders Johan Herbert. Legitimate. Westman Johan, Sailor. Mrs. Andersdotter Amanda Mathilda. Mother married. Age 40/32.
1882. Gustavi Domkyrka. Göteborg. No 1200. October 14. Male. John Hereberth. Legitimate. Father: Westman Johan Sailor. Mother: Mrs Andersdotter Amanda Mathilda. Mother married. Ages 42/34.
Harry Richard Emanuel
Entry 71. February 7 . Male. Harry Richard Emanuel. Legal status: legitimate. Father: Westman, Johan, sailor. G [probably marriage date] 30/3/73. Mother: Anna Mathilda Andersdotter. (O.H. 34.) Mother: married. [Ages?] 43/36. Medical attendant: "ex."
Josef Harold Moroni
No. 235. April 23, 1888. Male. Josef Harald Marone. 7th [child]. Legitimate child. Father: Westman, Johan, sailor. G 30/3/73. Age: 48. Mother: Mrs. Anna Mathilda Andersdotter. O. H. 8 ? 20. Mother married. Age 40. Medical attendant: "ex."
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I have looked through all the Göteborg parishes and other jurisdictions but cannot find the death records for the two children who died in 1881, Gerda and Anders.