Kiddushin 50 - Betrothal by a Liar
If a man says to a woman, "Become betrothed to me on condition that I am a Kohen," but he is found to be a Levi, or the reverse - even if the woman later says "In my heart I intended to become betrothed to him nevertheless," - she is not betrothed. Unexpressed intentions are not recognized in Jewish law.
If one betroths a woman and her sister simultaneously, neither is betrothed.
There were five women, two of whom were sisters, and a man collected a basket of their figs and said, "You are all betrothed to me with this basket," - the sisters were not betrothed.