Thank you for the advice, I hadn't thought to check all the birth certs of their children, they were all born in Scotland so I should be able to find them. And I will check the census records too - the snapshot you get on ancestry is very limited in detail. The death for May Ann Lackie sounds promising as they were in Dalmellington, so I'll check that too. I do find that sometimes when I search for BMD's I can get nothing & then other days I end up finding what I want!
Thanks again for pointing me in the right direction.