In the 1841 Ancestry Census for John (jnr.), he is styled: Mail Contractor, age 65, living in Cotton Street, Castle Douglas, with Jannet, age 50; Margaret, age 20; Isabella, age 20; Marrion, age 11; Jannet, age 7; James Coates, age 15.
In the 1851 Census he is styled: Retired Mail Contractor, age 76, living in Cotton Street, Castle Douglas, with Janet, age 64; Isabella, age 32; Grace, age 23.
In the 1841 Ancestry Census for John (Flock), he is styled Agricultural Labourer, age 55, living in King Street, Castle Douglas, with Grace, William, Isabella, Elizabeth and Robert, for which I have no ages.
In the 1851 Census he is styled Labourer, age 69, born Colvend, Stewartry of Kirkcudbright, and living in King Street, Castle Douglas, with Marion, age 30; Elizabeth Taylor, age 6; William Kerr, age 7 MO.
I think I have now pretty well exhausted all the information I have on the family but I would be interested to learn of your cousin's burial information.
Please let me know if you have any problems in deciphering!