I finally got a response from the Washington library Obituaries.
Thank you so much for your suggestion, they where able to send me a copy of my grandfathers Obituary.
It included some very helpful information, including the married names of his children.
I now know that as the time of my Grandfathers death in "1991" that one of his Daughters
Norma Jane Smith married someone called Sutton and they lived in Junction City, Oregon
The other Daughter Judith Lynn Smith had married someone called Shaffer and they lived in Vancouver.
I have not been able to find the marriage records for either of them though.
I also know from the Obituary that my Grandfather's son "William Henry II Smith" was also living in Silverdale, Kitsap, Washington at the time of his father's death. But I have not been able to find any further records for him either.
I would be so grateful if anyone was able to help me in any way