Sė Denissimo .. it is one and the same family for, as mentioned above, Raymond Guest was a cousin to the late great Sir Winston Churchill and was the son of Frederick Edward Guest who, in turn was the son of Ivor Guest (1873-1939) - see the last entry on the family tree on the lower left-hand side of the chart below:
As you can see .. Ivor Guest was directly related to John Guest (top of the tree) who worked as manager of the Dowlais Ironworks of Merthyr Tydfil in 1767. Under John's son Thomas, the Guest family's involvement in the works flourished with the works eventually becoming the largest iron rolling mill in the world (back when Britain was an industrial power).
There is a long (and interesting) history behind the family and .. in 1900 the mill and asociated businesses were formed into Guest, Keen and Co. - two years later becoming the Guest, Keen and Nettlefolds (GKN) to which you refer.