There is no John Cowley listed as a tradesman in Douglas in Thwaites 1863 directory there is however a J Cowley corn + flour dealer listed in 1852
Cowley J, Queen street - see http://www.ee.surrey.ac.uk/Contrib/manx/fulltext/qg1841/dir_52.htm
The genealogy of the Stanley family is at http://www.ee.surrey.ac.uk/Contrib/manx/people/lords/stanleys.htm
but to best of my understanding they sired no children on the Island until the Murrays