I think Frances is right, and Peter's Ann Cretney was most likely to have been Anne Margt bapt 18 March 1827 Lezayre, the illeg daur of Esther TAGGART & Charles CRETNEY.
And also that Peter was correct with her burial being: CRELLIN, Anne 31 German 20 May 1857 als CRETNEY [BL index].

There are still a few mysteries with John & Ann's baptised children, which could probably be sorted out by looking at the register.

Ann Cretney aged 15 was a servant in Arbory in the 1841 census, and was possibly Nancy Cretney (Crelney in Ancestry) aged 24, a House Servant, in Peel in 1851, but this gives her birthplace as Santon.

Sue