Gizzi I'm doing a biota revision on my Gibson part of the tree and have been on Rootschat to start with.
Alexander (born 1824 or 1833,depending on which record you believe - marriage or census) married Mary Anne (Marianne) Rosborough.Alexander's father was William Gibson of Carrick,Limavady,according to marriage lines.I can't find a William Gibson with son Alexander anywhere. ( There is a William Gibson and Margaret/Martha

with 2 sons Robert and John in 1824&1826 in Drumachose,but no Alexander)I have tried Scotland too, because quite a number of N.I. men went to Scotland for seasonal farm work in those days, but no joy.Their is also aWilliam Gibson and Hester/Esther ?? in Dungiven in more or less the right time frame, but no Alexander.
Alexander and Mary Ann Rosborough had Joseph who married Mary Anne Mc Cully,who had Joseph who married lily Poston who had David m'd ?? - (the rest you know !!)
Have you made any progress with William in the intervening years? ( my late husband,Jim Harper and David Gibson were cousins.Jim's mother Margaret, and David's father, were brother and sister.)