I have several baptism and marriage records from 1721 to 1807 that give the names of witnesses and godparents. Was it the custom to have relatives named on these occasions at that time? I know that it was in the French records.
As far as I understand, this is/was a standard practice of the Catholic Church anywhere. But, perhaps I'm wrong.
If names do not match, it is possible that the connection is through a female line. It is worth the time to track down the witnesses and sponsors. We have found a couple of female cousins this way, and suspect a third is a great aunt. For her, we haven't located the marriage document yet that would prove it.