Hi,
Welcome to RootsChat
I might have found the relationship between William RIGDEN and Henry SANDFORD,
Marriage10 Jun 1800
St Mary and Eanswith, Folkestone, Kent
William RIDGEN
Bachelor
Elizabeth SANDFORD
spinster
Both of this parish
By licence
Witnesses: John and Ann SANDFORD
Interestingly a John SANDFORD married Ann RIGDEN in Folkestone in 1799.
BaptismSt Stephen, Norwich, Norfolk
Wm son of Wm RIGDUM? and Elizabeth his wife late SANDFORD spinster was born 13 Apr 1800 baptized privately 15 May 1800
All of the marriages listed on this page have the "late xxxx spinster" wording, but this baptism was before their marriage.
Then I found this transcription of a will of a Henry SANDFORD of Cromer which mentions amongst other siblings his brother John SANDFORD and his sister Elizabeth RIGDEN
http://eastanglianancestors.co.uk/fam5838.htmlYou can pay to view/download the will at the National Archives,
http://discovery.nationalarchives.gov.uk/details/r/D19971So if William RIDGEN is the son of William and Elizabeth RIGDEN nee SANDFORD and his partner is Henry SANDFORD jnr the son of Henry SANDFORD Snr the writer of the will, then they would be cousins
Hope this helps
Regards,
Daisy