"Da" is more than likely "the." Many of the tunes from Shetland, for example, start off with "Da" eg "Da ship in full sail"; "Da smoky lum." I wonder if "middle small" might refer to fingers?. If the lady did not have a ring, she might have cut some of the her hair and made one that way. "You never bought them marrow" is probably telling the father that he had never got wives for the sons.