These Rankins are not the same family as my own ancestors.
Your Thomas Rankin married Christian Milne in the parish of Tyrie in 1803 (the marriage record is dated 21st August, but could be the contract rather then the actual marriage. You have to see it to know).
The 1841 census shows them at Bracoden, Gamrie, both aged "60" and born outside Banffshire. Thomas is an agricultural labourer.
The 1851 census shows them still at Bracoden. Thomas, 74, retired farmer, was born in Fyvie. Christian, 74, was born in Ellon.
They may have died before 1855 when compulsory registration started. If they were buried at Gamrie, the burial register was kept pretty accurately at this time.
Graham.