I presume you have obtained their wills (there are two possible Margt Quayle als Cowleys in Ballaugh - wives of William & Finlo. The will should also indicate the various children bapt before the PR included the wife's name (c. 1760). I also presume you have looked at the official copy of the Parish Reg on mormon film to see if any distinguishing locations were included. If any property was mentioned have you checked the manorial roll to see from whom Wm obtained it. Margaret's last child was 1770 thus likely she was born 1725 to 1735 - check out births in this period - I don't see a marriage in the IGI, one possible reason is that she married Wm Quayle as a widow - marriage could be under her married name whereas the children were under her maiden name (tho I didn't see any obvious match here either).