Cheapadar ó bhí ... They thought since he had the great name (i.e. King) that he would be "great" in every way i.e. generous;
mar tá ceal eolais ar shlite mar seo orthu - - because they suffer a lack of knowledge of/in ways like this. In other words it was a forlorn hope that he would have brought barrels of porter from the wedding for them.
Cheapadar = cheap siad; an fhoirm tháite in ionad an fhoirm scartha.