It wouldn't be surprising to me for the major lines to go from Havre, Liverpool, etc; 'feeder' ships ran from other destinations in Europe to the big ports for transatlantic travel.
The passenger lists are interesting, particularly 1912 into Ellis Island. Here, Villa Cote d'Azur, Nice is given as their 'home' address (putting them close to the border with Italy), although they sailed from Liverpool. In this record, they are both listed as born England, Louise in Wingfield and Violet in Lynton.
In 1909 Louise and Violet are both listed as born New York, when they arrive together with Hans.
https://familysearch.org/pal:/MM9.1.1/F6WC-P84 - now, could this be the marriage? Note the parents of Louise : Arthur and Sarah 'Culberhouse'. (In addition: Louisa Franks, married, aged 40, arrived on the same ship as Hans Winterfeldt, aged 32, in May 1905 - aboard the Saint Paul).
Now for this family in 1881:
https://familysearch.org/pal:/MM9.1.1/XQ71-WLHand the christenings of Frank (
https://familysearch.org/pal:/MM9.1.1/J385-39Q ) and Annie Louise (
https://familysearch.org/pal:/MM9.1.1/N1TD-3G8 )
Arthur Hill Druce married Sarah
Fortescue in 1861 (freebmd.rootsweb.com)
Sarah Culverhouse married Thomas Fortescue in 1854.
So if Louise 'Franks' who married in 1905 was the same as Annie Louise daughter of Arthur Hill Druce and Sarah nee Culverhouse, she had a connection to the Fortuescue family through stepbrother Frank.
In 1871, Annie Louise is with her Druce grandparents - she had an aunt, Annie Druce, who was 19 in 1871, perhaps the same as mentioned in her will? There were also two younger children - Helena Maria, born 1865 died 1879, and Arthur John, born about 1868 Windsor, Berkshire.
I'm fairly sure these younger siblings were the siblings of this Annie Louise as at
http://www.london-gazette.co.uk/search , Arthur Hill Druce's death/estate is mentioned along with Arthur John Druce
In addition, regarding the Annie Druce who was 19 in 1871 (so about 1852), there is in 1910 a 54 year old Miss Annie Druce (born Kingston, Surrey), last residence in the UK with a Mrs Crussell in Huntingdon, heading to her relative, Mrs Winterfeldt, in New York.
It seems possible that Violet was Annie Louise/Louise's niece, through one of her stepbrothers. Have you seen the Ellis Island entry where she is listed separate from Hans and Louise, as 'Winterfield Fortescue' (no first name) in 1906?