Witnesses to a wedding can be a family history clue, but there are a few things to keep in mind before assuming that witnesses have to be related to the ancestral couple who got married.
Witnesses legally are just saying they saw something happen and that they know the individuals who are they claim to be. The witnesses do not have to be related in any way shape or form to the people getting married.
The witnesses can be friends of the bride or groom–perhaps even an engaged couple themselves. The witnesses could also be the wife of the officiant and another nearby warm body old enough to legally be a witness. They could even be the parents of the couple.
Unless the parents were vehemently opposed to the wedding, then probably not.
But don’t assume the witnesses must be related. Even if one of them has the same last name as one of the parties getting married, there may not be a relationship.
Like anything else, names of witnesses are clues.