Hi Viv , I am a little confused , you started this thread looking for John Taubman Caine , On the IGI are the following births in Onchan , all from church records,, to John Thomas Cain and Margaret Jane XXXXXX :

1864 Catherine Ann
1866 John Taubman
1868 Alfred William
1871 Agnes Louisa
1872 Jessie

1881 Census (free IGI transcribed) Ballachrink Onchan

John T Cain Head Marr Male 45 POB Onchan
Margaret Cain Wife M F 30 Santan
John T Cain S U M 15 O
Alfred Wm Cain S U M 13 O
Agnes L Cain D U F 11 O
Jessie Cain D U F 9 O

So John T and Margaret were both 33 in 1871 and 45 and 30 in 1881 ???? as Frances pointed out is this a different Margaret in 1881 ?, as it means that she would have been 13 when Catherine Ann was born in 1864. Perhaps someone can check original 1881 census to check age .

John Taubman Cain was buried 18/12/1921 in Jurby (Lawsons) , so perhaps you need this death certificate

But I don't think there is any doubt that the John Taubman Cain christened 1/1/1867 is the one at Ballachrink in 1881 , most unlikely there are two John Taubman Cains born circa 1866 in Onchan .

Can't find what happened to Catherine Ann Cain.

Annie Elizabeth Forsythe appears christened 16/2/1873 Jurby to Hugh Forsthye and Ann Jane Cowin , strange she did not call any children after her parents.

Cheers
David