Christine, I have been trying to research a Robert Costain but didn't get very far with him. 'My ' Robert died March 1868 age 49 which would give him more a 1818/19 birthyear. He md Ann Archibald in Malew in Dec 1844 & I'm descended from their dau Eliza(beth) Jane. In the 1851 census both Robert & Ann were aged 31 & living in Douglas. In 1861 Rbt was 42 & a roper at Culloden Place Douglas. Robert is given as Castletown for his birthplace . I have a ? for Robert's parents - a Robert Costain & a Mary Christian but no verification because earlier than 1851 census has been tricky to sort him out. Maybe he is the brother of your ancestor.