Hi, you may be through your brick wall by now as this is quite an old post. I was intrigued as you had a Nicol and Careston is a family area. It looks like there may have been a name change, and was the death certificate correct?
David Buchan and Jean Dildarg / Dundass seem to be having children in Careston in the 1810 to 1820 period. He recorded as Wright in Craig, so it looks like the same family.
David Buchan, Wright in Kirkton is having children in Menmuir, including Alexander, so that looks right as well.
Next -
Jean Dildarg to William Dildarg and Ann Nicol in Brechin, 20/10/1781
I note also that there are other people who have noted the Dundas / Dildarg name change at about the same time, also Dargie.
I hope this helps