Both 1851 and 1871 census have that William's birth place as Beverley Yorks
so possible baptism:
Name William Milner
Gender Male
Christening Date 12 Sep 1802
Christening Place SAINT JOHN AND SAINT MARTIN,BEVERLEY,YORK,ENGLAND
Father's Name James Milner
Mother's Name Mary
Mary is recorded as being born Beeford so:
Possible baptism for Mary Morris:
Name Mary Morris
Gender Female
Christening Date 09 May 1802
Christening Place BEEFORD,YORK,ENGLAND
Birth Date 05 Apr 1802
Father's Name John Morris
Mother's Name Jane