Could you at least try to calculate an approximation of when Philippe/Philip Coutanche was born in Jersey.
It depends on your age... I am old and my own grand-parents were born around 1880-1895. I have no idea if you are young or old, but I can try to find that birth in Jersey.
I found a Philip Coutanche marrying in Liverpool district in autumn 1906. The index (on www.freebmd.org.uk that you can search for free up to 1983) name all the people on the page which has only 2 marriages, therefore 4 people , so his wife is either Mary O'Brien or Elizabeth Williams. If you know your grand-mother was Mary, then it COULD be them.
On the 1911 census, there is a Philip Coutanche aged 27 (= born around 1884) but born in Liverpool. However his father John is born in Jersey... The first child is called Mary aged 4, which corresponds well with a marriage in 1906..
Curiously this Philip is married with 4 kids but his wife (surname O'Brien for the twins Ruby and Delia, according to another official website) is not there that census night. I am trying to attach image. Let me know if it is readable. The twins died later in 1911.