Maybe Jean is a sister of his mother?
Look at 1841 census in Coupar Angus, a David and Agnes Ross (your James' parents?) living with a Jean Geekie ... David is still alive on the 1851 census still in Coupar Angus, b. 1767 in Tain, Ross shire
If you look back on the FDCA page listing deaths in Dundee there are two other chaps named Ross, born in Tain of a similar vintage to David that might be worth investigating ...