Have you tried requesting his death certificate?There are entries for the names of both of his parents.
For a death in 1918, it should be available from the Ohio Historical Society for $1.00.Start at http://www.ohiohistory.org/dindex/search.cfmhttp://www.ohiohistory.org/dindex/search.cfm and find the volume and certificate number, then follow the "Obtain Death Certificate" link.
Or you could request a certified copy from The Bureau of Vital Statistics, 601 Lakeside Ave., Rm. 122, Cleveland, OH 44114.(216) 664-2317.I think they charge about $10.00.