Hi Harry,
The information on both father and son is on FindMyPast.
It appears that WR Whytock senior first joined the 11th Hussars at the age of 18 on 14 August 1900 but was discharged on 10 September of the same year, I have yet to find the reason but it may be on health grounds as he was admitted to hospital with inflammation of the tonsils in September. His father was noted as Richard Whytock of 10 West Preston St, Edinburgh, along with the names of his brothers Richard, James and Alfred. His occupation was shown as shoemaker.
Then after the outbreak of WW1 he joined the Royal Highlanders with the regimental number 201875, which being a six figure number, suggests this was from 1917 onwards. He then transferred to the 1st Battalion Black Watch and served in 10th Platoon, C Company. On 18 March 1918 he was reported to be a Prisoner of War and in a camp in Germany. He was probably taken prisoner during the German counter attack in Feb 1918 following the 3rd Battle of Ypres.
Based on an Edinburgh Gazette notice dated 12 August 1938 I'm guessing that his wife had recently died as he was trying to get administration (not the Scots legal term for it) of her estate. Her name was Eliza Jane née Brown. WR senior's address was given as 2 Lasswade Road, Liberton.
A newspaper notice from later that year said that William Reid Whytock, younger son of Mr and Mrs WR Whytock of Lasswade Road, Liberton married Euphemia Duncan, younger daughter of Mr and Mrs Thomas Duncan of Jubilee Road Whitburn, on 12 August 1938.
Not wishing to spend lots of money on credits for Scotland's People that is the extent of my research.