Sanhedrin 28: Yevamot for Witnesses
Relationship and relationship charts are the essence of most of this daf. What relationships disqualify relatives from testifying against or about a relative? Note that these are all men - as witnesses, though some of the relationships include in-law status via women. And note that these are not the same relationships as the prohibited marriage/yevamot relationships. Also, a "lid on a barrel" - the mechutanim (fathers of bride and groom) can testify against each other. But can a man testify against or about his betrothed? Is that too close of a relationship? But he wouldn't be in deep mourning for her if she died (nor she for him).