Have looked at the service record myself and I don't think these are sisters of James William. The information for them is shown in the aunts/uncles box together with a Patrick Gavin.
Trees on Ancestry show that a David William Conniss married a Bridget Gavin and children shown as:
Edward Allen Johnston b.1883 Galway
John b.1884
James William b.1886
David James b.1888 (died?)
Samuel John b.1888
David Robert b.1890
Mary Ann b.1892
Father David Conniss shown bc.1857 Carraroe, Galway, d.Mar.qtr. 1894 Oughterard, Galway.
Wife Bridget clearly remarried after but was deceased by 1901.
1901 Census - Rusheenduff, Rinvyle, Galway
Mortin Cannon, widower 47 Hawker
Edward Connis 18 Shoemaker
James Connis 14
David Connis 11
Mary Anne Connis 9
Belinda Charlotte George Fleming, widow of William Fleming, d.1/8/1944 Mill Street, Glasgow.
Shown as daughter of Samuel Connis, Shoemaker (deceased) and Jane, nee Best, (deceased).
This matches the birth found in London and therefore suggests they could the parents of JW'S father David Belinda was indeed his sister (and JW's aunt). I'm also wondering if the 'Lucie' is actually Lucia (looks like that to me on service record).
Finally, what an awful surname it is to pursue in the records - so many variations.
Annette
PS I see others have been following my thoughts but will post anyway.