Hello -- info about your grandfather on the Commonwealth War Graves Commission website at http://www.cwgc.org/
confirms the names of his parents. It states "Son of John and Sarah Jane Coleman; husband of Annie Hester Kate Coleman, of, Gillingham, Kent."
To access this info yourself, click on the Search Our Records link which is listed on the left side of the CWGC home page. Regards, Andrea (Kent Board admin)