As the 1861 census indicates that James first child aged 12 was born in Liverpool to a non Manx mother. it is probable that James had left the island before 1848, and possible that he had left before the 1841 census. This would explain his absence from the 1841 census.
Also in Frances' Manx notebook, check Pigot's 1837 directory as there are some Gellings in Douglas.
Edward on Queen Street
John on Great Nelson Street
Richard on Woodburn Road
Thomas on Cattle Market Street (Bootmaker!)