I'm interested in this couple also. Their son Robert Black, brother of Mary is of particular interest to me. I think Helen is the daughter of James and Janet (Russell) Leishman born 1772 in Falkirk. I believe her paternal grandparents were William and Helen (Johnstone) Leishman (possibly whom she was named for?).
Leishmans back to 17th centuryhttp://wc.rootsweb.ancestry.com/cgi-bin/igm.cgi?op=PED&d...
William's parents were Robert and Agnes (Muir) Black, but can't get earlier than that.