The only possible burial for Thomas Bannan on Brian Lawson's burial index is:
BANNON, Thomas And 24 Aug 1827
www.iomfhs.im/lawsons/burials/ba_01.html
Wife no.1 is there as BANNAN, Catherine, Andreas, 3 Dec 1798, [als] LELAGHAN, but did Cath Christian
leave Andreas after her husband's death? Or remarry?

Sometimes the wife is named with a second husband in attachments to her first husband's will
(re. disposal of property, etc.), but I can't find any Bannan wills at all - which seems odd, unless they
have been indexed wrongly.
I would have expected a decree for Cath no.1 who was buried on 3 Dec.1798, the day after the bapt
of her son James, and apparently leaving several underage children.
Thomas remarried on 7 May 1799, in Andreas. I'll find out whether the marriage says what parish
she came from.

Sue