FamilySearch has a baptism of a Robert Sainsbury 23 Mar 1766 at Westbury, parents James and Margaret, and another 2 Nov 1766, parents Robert and Mary. Then findmypast has some Robert Sainsbury burials at Westbury in 1766 and 1773, so maybe one of those is one of the two baptised in 1766 (or maybe they both are
) I don't have a sub to see what info there is on the burials.