Thank you Kay99. Other people have also responded to me about William. I appreciate your input.
I have since learnt about a 1934 newspaper article regarding his death. It states that William's father in law L A Challicom was in attendance. That would suggest that Lillians birth name would be the same. Also in the article it mentions his step-sons Gordon Collins and Bert Collins.
In the 1921 census there is William and Lillian Rees with Sydney, Leonard, Bert, Gordon, William, Reggie, Cecil. I'm about to purchase a marriage certificate between William and Lillian which will hopefully point me in the right direction. Regards Elaine