I suspect confusion reigns (after all you have now posted under 4 or 5 different names!) - Richard Cain owned (ie had majority shareholding there would have been other shareholders) and ran Castletown Brewery (he sold out in late 1930's) - Cain's Brewery was in Liverpool and was operated AFAIK by an Irish Cain family - the Castletown Brewery would have employed several men (though I believe breweries were actually not big employers as such, most jobs would be in the delivery trade) though the chief brewer was Richard Cain's son who remained there after the take over;
(other on Island breweries were Clinches and Okells in Douglas )
I do have a W Potts CTC JP recorded in 1903 (leading an IOMNHASoc excursion) - CTC may well be Castletown Town commissioner (the chairman of whom was ex officio a JP), he does not appear on my later lists of JP's so it is possible that there was a Potts family in Castletown pre WW1, however I have very little post 1918 info