The witness Ewan Kneale looks like Esther's father or brother. Ewan son of Ewan Kneale & Margt Caley, bapt 27 Dec. 1791 Lezayre [IGI]. Esther bapt 12 Aug.1785, same place and parents. Her age was given in records as b.1786, 1787, and 1788, so pretty close. There were also two Esther Kneale bapts in Ramsey around the right years, but no Ewans.
Additionally, William & Esther had children Ewan and Margaret Benson.
What was the bapt date for the William you found? "wm noted in Malew register to Wm Benson + Ann Dawson".
I found only that couple's daughter Ann.