I think you need to give us more information on William, where did he end up ? Where and whom did he marry.
On the 1841 census there is a Sayle family in Kirk German at Strand Street, with the Greggor family :
This William had married Jane Greggor in Kirk German 12/7/1840, and therefore living with his in laws.
Isabella aged 64 is at the same place with a different (Irish) family in 1851, as a WIDOW, a Dressmaker, born Peel.
William is also in Strand Street aged 32, shown as a mariner , with wife Jane and 3 children
There is a burial Kirk German 22/12/1856 aged 73 - a little out - Shows maiden name Christian.
Possible marriage 9/5/1815 Braddan Isabella Christian to John Sayle.
Can't find William and family on 1861 census