My Great-great great Grandfather's brother, John Hignell, married Rachel Prosser in 1843. Rachel died in the first quarter of 1850, leaving John a widower with a young daughter, Ann. John Hignell then married Ann Waters, nee Prosser in December 1850. By a strange coincidence, it took 17 years for the Prossers to pay Rachel Prosser Hignell's bequest to her Husband.
Was Ann Prosser Waters Rachel Prosser's sister or cousin? If they were sisters, was it legal to marry your sister in law by 1850? I think the best bet would be to get the GRO record for both of John Hignell's marriages and see if the brides had the same father with the same profession. I'm well awar of the many people in Monmouthshire with the same names.