Were you able to trace Robert Ritchie/Smith b. 1904/5 on the 1911 census?
No. There are too many Robert Smiths in the 1911 census to do it online. I was hoping I might get into Register House some day soon but that has now evaporated in the meantime.
Did his mother remarry maybe?
She may have done. There doesn't seem to be a death in the SP index. I think she may have had Irish connections as her father's name was Sandford St Arnaud Warburton and there are two marriages of a man/men of that name in Belfast, both after the date of her parents' marriage. Her mother was Agnes Broomfield Smith.
George L Smith is easier. His father's name is hard to read but looks like Lowthe August Smith, and his mother was Mary Amelia Gill. There is a Lowther Augustine Smith married in Weymouth in 1856 to Mary Amelia Gill, then Mary Amelia Smith, aged 38, died in Portsea in 1872, then Lowther Augustus Smith married Rachel Luke in 1872 in Portsea, and died in 1889 in Alverstoke. George Lowther Smith was born in Stoke Damerel in 1870, so would have been exactly the age of Robert's father; and the birthplaces fit with Lowther Augustus Smith being a boatswain in the Royal Navy. However he doesn't seem to have died in Scotland.
Hope that you have been able to make some progress with Jean herself!
None at all. In fact I have no idea where to go from here, really.