Yes, I agree that the 8 yr old gdau Ann certainly looks like John & Ann's eldest daughter, and it is very interesting that Philip Corkill and wife Ann Kelly had an eldest son John bapt German 13 Sept 1812.
I thought that the John Corkill of Greeba who was buried 11 Feb.1847 was the most likely John C. to be the one Rob was looking for. The age 33 wasn't far out to be the one you found, because being bapt in Sept probably means he was still 34.
I had found three marriages between 1847 & 1851 which I thought were possibly what had happened to his wife Ann (in Braddan, Marown & Andreas), but only one appears to have been scanned - the others were not on the MM site or FamilySearch par regs. She was a spinster at the Braddan marriage, so not her, which leaves the other two.
Sue