I have now received a copy of Jacob's marriage certificate. He was married on 10 May 1885 at Newton Abbot Register Office.
Jacob Langwasser, age 22. Bachelor, musician. Of 1 St Michael's Terrace, Torquay. Father - Peter Langwasser, farmer. The witnesses were the bride's brother and sister ( my great grandmother). This occupation is not repeated on any census.
This would appear to eliminate Adam (1862) who, coincidentally, was described as a musician when he entered United States in 1887 as a member of a band.
If, as seems likely, Jacob was illegitimate I think the declared identity of his father should be approached with caution.
I'm not sure if any of this takes us any further forward but would welcome any inspired suggestions.