This man joined the army as James MARTIN, so is "mis-filed" in the WW1 Service Records (WO 363):

KINNEY, James: Birth registered Q1 1884 (Cockermouth) - unmarried mother Mary (b c1863)
Mother married a MARTIN.
Residence 1905: Dearham, Cumberland
Residence 1919: High Spen, Gateshead, Co Durham

3 half-brothers (all born MARTIN)- c1886, c1894 & John;
3 half-sisters (MARTIN) - Elizabeth c1893 (married by 1919), Xx Ann (c1901) & Mary (c1903)

James joined the Northumberland Fusiliers on 1 August 1905, declaring previous service in the Army Service Corps (no details). Regt No. 18508.
Transferred to the Border Regiment (Regt No. 8993), progressed to Sergeant, and was killed in action 1st October 1918.

Anc****y, MAR, pages 200564-200576