Note that this is a marriage licence, not a marriage. Three possible parishes are given for the marriage - the license was only "good" for those parishes. If you can't find the marriage in one of those, they may not have ended up actually marrying.
On a license, there was a bond to pay if it turned out false info was given. The allegation (affadavit) refers to the information given, and the person(s) alleging were putting themselves up for a serious financial penalty. Normally a relative or close friend of the groom.
Here, Thomas Mackadam could be any sort of relative, father, uncle, older brother, grandfather of Daniel.
