Sorry, been without internet for a few days ...
Children have various mother's maiden name, so yes, I see your confusion!
Emma COOPER - 1869 -mmn GREGORY
Alice COOPER - 1867 - mmn DIGGORY
Ann COOPER - 1865 - mmn DEGGORY
James Cooper GREGORY - 1861
Elizabeth GREGORY - 1859
Mary Ann GREGORY - 1857
I think as the marriage has GREGORY, it sounds like this is correct. Pronunciation and spelling may account for the variations.