OK, got it! The good news Tony is that you have more aunts than you thought! Unfortunately were some infant mortalities. Here we go (I'm including references in case you want to pursue any certificates for confirmation etc):
Your grandmother was Ada Curtis, born in Birmingham, June quarter 1885 (Birmingham 6d 11), daughter of Amos and Rosetta Curtis.
The 1891 census shows her with her parents and sisters Alice and Ada, at 4 back of 36 Sheepcote Street.
The 1901 census isn't quite as clear, but she appears to be working as a servant in Balsall Heath, claiming to be 18 (in fact she was 16).
She married Frederick Percy Harris at the Birmingham Registry Office on 16th December 1905 (December quarter 1905, Birmingham 6d 332), one witness being Rosetta Curtis, presumably her mum.
The 1911 census return I mentioned above is correct - in that year they are living at 3 back of 24 Grosvenor St West, Ladywood. Ada is 26, Frederick 27. Three births are listed but only two surviving, so sometime before 1911 there was an infant death.
Frederick's First World War army records have survived (service number 43427), which state he enlisted as a gunner in the Royal Garrison Artillery on 18th August 1914 for eight years, aged 29. He gives his occupation then as "Civil Occupation (Engineer)", and appears to have served at Woolwich, then at Le Havre. By 1914 the family are living at 2 Park Place. The records include death records of two more of his children.
These are children I found:
Ada, born 16th December 1907, died 21st February 1915, aged 7, of acute laryngitis and bronchitis (certificate included in father's service records).
Frederick, born 6th January 1910
Dorothy A ("Doll") born 17th Sept 1911 (December quarter 1911, Birmingham 6d 26)
William - born 1st July 1914, died 21st February 1918 (certificate also in father's service records) aged 3, of meningitis.
Francis - born 8th January 1916 (March quarter 1916, Birmingham 6d 280),
then your father William (June quarter 1920, Birmingham 6d 470).
Later on there were twin girls born in June quarter 1927 - Rosetta (Birmingham North 6d 517) and Violet (Birmingham North 6d 516).
If you direct message me your email address I'll send you a copy of the census and Army service record.