Hello Ian

John Waterson/Watterson's will in 1794 names children William, Patrick, Margery and eldest daughter of Thomas "Pekey". He died Feb 12 and gives his residence as "Corvala"
You have him born Malew 1724, but I could not find his birth , however I found births for John and Margery - 1715 James, 1723 Jony, 1725 William, 1728 Edward and 1731 Patrick.
The LDS IGI birth for Edward shows mother Marjery Watterson or Corvalla. This is an error as Corvalla is the residence , and the handwriting shows Corvalla in brackets like the previous birth which showed residence as Balla XXX.
Patrick is not a common name in this period. The period 1700 to 1800 shows only 5 Patrick Waterson deaths including two infants in 1785 and 1797. So the fact there is a Patrick in the two families binds them together.
Having said that, there are multiple User sponsored trees on the IGI showing the parents of your John b circa 1724 as Patrick Watterson and Margaret Watterson (Nee Watterson) and one or two have Margaret as Marjery.
Hope this helps
David Dwyer