You are wanting to take this family back through the censuses?
FreeBMD does not have a birth registration for a George Henry Taylor in 1868.There is this one
Births June 1/4 1867
George Henry Taylor Stoke Dameral Devon vol 5b page 349
Ada was his first wife born c1866 in North Tawton Devon also. So did she die after the 1901 census? There are quite a few deaths for an Ada Taylor 1901 to 1908 when he seems to have married Nellie.
There is only one marriage of a George H Taylor in England and Wales 1908 to 1910 and this is it
Marriages Sept 1/4 1908 Nellie Alexander to George Henry Taylor Swindon Wiltshire 5a 14
There are other marriages for a George without a middle name or with other middle names. George did seem to move around a bit. Phillip born in Islington, Alice in Southend Essex and John in Forest gate Essex.
You really need a birth certificate for a child of Ada and George and one for a child of Nellie and George These would give you the maiden names of Ada and Nellie. The marriage certificate for George and Nellie would give you George Henry's father's name.
Oh and welcome to Rootschat
