Remember all obituaries are not always 100% correct, one for my wife's Grt Grandfather William Pyke said that he had came to New South Wales from England as a young child, when he was actually born in Newcastle, New South Wales. Obviously
he wasn't around to correct the error. So John's Obit may not be correct.
No doubt James, Catherine , John and Margaret are siblings, their Obits DOB match their christening dates on the Isle of Man.
Margaret's Find a Grave in Omaha, Nebraska shows DOB August 22, 1842 , Christening date September 4, 1842.
Interesting 3 of the 4 siblings married other Manx people - Kinrade , Corlett and Killip. Could not find a birth for Julia Corlett on the IOM around 1832.
So the missing siblings are William (1824) and Robert(1832), double checked Robert and there is no death between 1832 birth and 1841 census. There is a burial of a William Kermeen in Maughold October 7, 1846 , but no age is given.
Could not find a burial on the IOM for James and Mary Sharp.
Some other posters may be able to confirm death of Willam and the marriage 1855 of Widow Mary Kermeen