My name was given me because I was due to be born on Saint Davids day therefore I have no special knowledge of your relation. If there was aristocracy involved then I would start with Lord Glenconner and his ancestors Sir Charles Tennant etc.
The first Tennant with the title Lord Glenconner was Edward(1859-1920) but this branch had been making lots of money in Ayrshire from about 1800. David was a fairly common name in that family eg David(1762-1839) m. Anne Green. David (1734-1823) m.Katherine Dalrymple. had son William & d. Wilhelmina. Above info from "Tennant's Stalk" by Nancy Crathorne SBN 333 138201 1 Also "Broken Blood" by Simon Blow ISBN 0-571-13374-6