Johan Severin was born in Tegneby parish in Gothenburg /Bohus county. His father was Johan Martin Jansson b. 1849-02-26 also in Tegneby. His mother was Johanna Sofia Johansdotter b. 1854-03-13 also in Tegneby.
I have found six sibblings: Olle August 1880-08-26 (probably the August you mentioned), Clara Martina 1882-08-16, Conrad Samuel 1885-01-07, Hanna Elisabeth 1887-02-07, Gerda Maria 1889-09-12, Emma Sofia 1891-06-28.
I hope this helps you.