Hello Xanthe,
The photo is of Grave No. 2nd.Con.3596, Helen (1914), Edward William (1923) and Edith Rose (1968). That is the only gravestone you will find, but I have located two of the other three graves and have a fair idea where the third may be.
The photo below is looking towards the location of Grave No. 3rd Con. A67 where William (1914) is buried.
Bear with me as I have just got back from a second trip to Greenwich. It may take me a few days to put all the info and photos together.
Phil