Hi Do you have John Wardlaw's baptism cert 18 Sept 1873 from Irish Genealogy? (http://churchrecords.irishgenealogy.ie/churchrecords/details/d1f64e0559024). You will see it says father WILLIAM DAVID WARDLAW and mother MARY ANNE WARDLAW, which could mean that they were, in fact, married. William David is a Clerk in Bank of Ireland, like your David William Wardlaw, so looks like it's the same man - unless they were brothers working together???? Colette