Hi Viv , Jeff Wilde has provided the original copies of 1871 and 1881 census. John Taubman is shown as John Thomas in 1871 and John T in 1881 , Margaret is 33 in 1871 and born Marown , she 30 in 1881 and born Santon.
So it is looking more like there are two Margarets
On Brian Lawsons burial site , there is a Margaret Jane Cain , buried Onchan , 17/6/1878 , aged 42.
On the IGI there is a marriage of John Thomas Cain to Margaret Kneale , 8/10/1878 , in Santon .(strong confirmation of 1881 census)
There appears to be a least two children for J T Cain and Margaret Ann Kneale , both Onchan ( on Brian Lawsons site )
Frances 14/11/1882
Thomas 22/11/1885

Cheers
David