After 10 years, I hope that this is still relevant.
Picking up on your lack of information about James Gibb, I can confirm that he married Katherine (not Cathleen) Phelps, and lived for the rest of his life in Lydbrook in the Forest of Dean. He was a clerk/office manager at Cannop colliery. Incidently, I never heard of a brother owning a mine in the Forest - perhaps a garbled understanding of James' position?
James and Katherine had 3 children - John, Isabel Horne and Robert Forbes (plus a stillborn or very short lived child between Isabel and Robert.)
Isabel was a career nurse, and never married. She died in about 1993. I knew her well - behind a rather fierce exterior lay a heart of gold.
John became a teacher and lived for many years in Hartlepools with his wife Doro (presumably short for Dorothy.) He had 3 children - Tim (a soldier who was killed in Aden in the sixties), Andrew (a merchant seaman) and Judith (another career nurse until retiring to raise 2 children.) He died in September 2006.
Robert served in the navy in the war and was decorated. Subsequently he married Heather Evans, became a solicitor in Upminster in Essex and had 3 children - Richard Forbes (born 1950), Michael (b 1953) and Sarah (b 1959.) He retired to Italy with his second (Italian) wife, where he died in 2001.
James died around 1960, but Katherine lived to be 99, finally dying in 1984.
James' name lives on in my son, born in 1992.
I have a picture of the Gibb family dated 1908, looking very prosperous. However, family legend says that William Gibb went bust soon after, and James had to leave accountancy college and find a job, eventually settling in the Forest of Dean. I was very young when he died but I remember being very impressed that he could add up pounds, shillings (20 to the pound) and pence (12 to the shilling) in his head.
Let me know if I can offer any further information.