I checked the 1841 census - the two families (heads of which indicated as agricultural labourers) were adjacent in Lhergy dhoo (about 2 miles to NorthEast of Peel) - that of Henry were all marked as born in Ireland.
I found James in IGI transcription of Malew reg as James Cowin son of James Mc Cary & Isabel Cowin in Malew - it is thus possible he was born to one of the several Irish families who escaped to the Island c. 1798 to avoid troubles in Ireland or more likely to one of the many soldiers stationed at Castletown (a check on the register should confirm an illegitimate birth which is implied by the form of the IGI entry). The next family in Lhergy dhoo also had an Irish head - Charles Coffee