From the website "but was living with Gertrude Bell in Hull in 1909 when they had their first child"
If, as you say, Emily Grace was born in 1907 then she would still have been the child of the first wife. Maybe you have dates incorrect.
If you are interested in George's parents then, as previously advised, your first step should be the marriage certificate.
Or the certificate of George Rushton and Rose Annie Chell, details being December quarter 1900 Stoke.T. 6b 395.