there are several Corkill wills in Braddan or Onchan I've not seen - look at index/transcriptions on Brian Lawson's minisite (www.iomfhs.im) + my summaries on MNB
The only unusual name in the familiy is Peter so that may have some significance - eg a Wm Corkill + possibly Margt Corlet had amongst other children Wm, Peter + John - possibly his will is 1757 - remember that burials/wills for Douglas come under Braddan, property/civil records under Onchan