presume you are researching Thomas Bannan + Cath Lennaghan (other spellings available) - her will/decree states d Dec 1798 all children under age (ie not yet 14) except John - no marr on Island + three children John, Mary + Elinor in will but no bapt on Island - earliest on Island child bapt Apr 1791 thus probably c.1788-1790

There is a marriage of a Mary Bannan in 1783 in Rushen but prob not your family?