** UPDATE **
I have found the marriage certificate I knew I had.
On it, William lists his father as Job Kirkland (still alive), a Brick Maker.
And Mary Jane BAKER (aged 19) lists her father as Joseph Baker, deceased, a Labourer.
Had a look and can't find anything for Joseph so I've ordered what I believe to be Mary's birth certificate. Fingers crossed!!
I've also looked as their oldest daughter Lily was born October 1876 (marriage is December 1876)....