Bruce, I think that you have just helped me on to the right branch of my tree. My John Sansbury, a mariner, was unmarried in 1841. By 1851 he had married Ann and had four children Jane, William, Margaret and Edward. This corresponds with your information i.e. correct age, occupation, wife's name and children's names. Going on the IGI listings I agree that the only parents feasible are Richard Sansbury and Margaret Gawne. The only thing that surprises me is that none of his sons (he had three more) were named after his father. I am also grateful for the information concerning the deaths of Margaret and Richard.
Jane - do we have relatives in common?