Hi Jackie, and welcome to the thread! I have double checked my database, and like you, I don't have a marriage or death date for either Alexander or Mary, and I only have the one son noted as well - Lachlan, born abt. 1807 in Sleat, and died April 11, 1885 at Teangue. But there must have been other siblings along the way.
Lachlan and Mary's Daughter Margaret - b. 1839. married my relative Hector McLure Nov 1, 1881 at Sleat