I need to delve into this a bit more but as you are aware I have been looking into the Creer connections and have it so far as follows.
William Cubbon baptised 6 January 1795 as William Radcliffe, (Mother Margaret Radcliffe b1766 who married Robert Cubbon 7 February 1795) was transported c1848 for forgery. William Cubbon married Margaret Kerruish 20 October 1827. It is their daughter Isabella who was living with her Grandfather John Kerruish you mentioned on 1841 Census. Margaret Kerruish Cubbon is in 1881 living with Catherine Creer Casement and family as Aunt aged 76 so born c1805. (Cathererine Creer Casement being the daughter of Edward Creer and Esther Cubbon, Esther Cubbon daughter of Margaret nee Radcliffe and Robert Cubbon),
Therefore, Margaret Kerruish bc1805 was the daughter of John Kerruish and Isabel CREER according to IGI. No Margaret listed around this time to a John Kerruish and Ann Kinrade.
Isabel Creer according to IGI was baptised as you rightly say 2 April 1782 but maybe born a bit before that date...was marrying underage always recorded? Wasnt the legal age 14? If they married 1802 she could have been 18 - that would have been possible wouldnt it. Given that this Isabel Creer was the daughter of John Creer and Mary Corkill it is also likely that the Edward Creer (lived Ballavaston, Andreas) I have marrying Esther Cubbon, born c1785, is also the son of John Creer and Mary Corkill who I hadnt been able to establish parentage of so far but had noted this possible parentage a while back. Mary Corkill died 1785, noted in her Will (courtesy of Francess site).
1786-1 E d CREER Mary corkill d 7 dec 1785;8 ch William, John, Edward, Esther, Margt., Ann, Mary & Isabel Creer (most ua);husb john;pledges peter murray + peter corkill;
Hope this makes sense!
Sandra