Douglas was in the ecclesiastical parish of Braddan but mostly in the civil parish of Onchan.
At this period the two Douglas churches of St Matthews and St Georges were officially chapels of ease thus not licensed for marriage (marriages needed a special licence) - thus most Douglas marriages were at Braddan (those residing in what became North Douglas used Onchan).

St George reg tended not to give woman's family name thus identification always a problem

Hugh may well have been mistaken in choice of marriage though I would have expected him to know his mother's maiden name - there would be more info in the parish reg (borrow the mormon film) though at this period it would not give parent's names. Both marriages I quoted were indicated as extracted from official copy in IGI (I have personally only checked upto c.1800)

The bapt of Sarah in Malew could help collaborate a Castletown connection but no bapt I can see - where did you get the Ballaugh connection from