I see your quandry

1891 Census
Clifton Hampton, Oxfordshire
RG12/980/59/15
Richard BALLARD, 57, Head, Mar, Farm lab, born clifton Hampton, Oxford
Olive, 51, Wife, Mar, born Steventon, Berkshire
Henry, 21, Son, Unm, Farm lab, born Clifton Hampton, Oxford
Edwin Jas TERRY, 15, Gr son, Farm lab, born Milton, Berkshire
Ernest E Ballard, 13, Son, Unm, born Clifton Hampton, Oxford
On the 1901 Olive is his Mother and Michael (sic) Ballard his Step father
RG13/1133/44/1
Could be an enumerators mistake?
From my experience illegitimate Grandchildren could be brought up as children of the Grandparents.
I have never seen one Christened as the child of the Grandparents though.
I think you need his Birth Cert and Marriage Cert and Death Cert to try and confirm anything and put your mind at rest.
Marriage;
Edwin James TERRY, September 1896, Abingdon, 2c 545
Annie STEVENS only spouse.
Birth;
Edwin James TERRY, June 1876, Abingdon, 2c 306
Cheers,
Trish
