England and Wales, Census, 1851 · FamilySearch
For William Stacey & Charlotte Clamp
William Stacey | Father | M | 36 | Therfield, Hertfordshire; Charlotte Stacey | Mother | F | 35 | , Cambridgeshire; Mary Ann Stacey | Sister | F | 5 | Barkway; Sarah M Stacey | Sister | F | 3 | Barkway; Oswald Stacey | Brother | M | 0 | Barkway
The 1851 Barkway household as listed against Fanny E Stacey's record, quoted as relayed; the words Father, Mother, Sister and Brother are stated relative to HER, which is what makes both the parent links and the sibling set. The marriage itself is not evidenced - absent from the FamilySearch Hertfordshire records, and the two plausible FreeBMD refs for a William Stacey (Wisbech 1839 Jun vol 12 p.217; Biggleswade 1840 Dec vol 6 p.130) were not tested against a Charlotte - so the union type stays unknown.