Commentary for Kiddushin 130:3

A twisted scenario indeed. Both men have to give her a get, which means we must have some degree of certainty that they are married to her. But if either has two witnesses, then how could she claim, “These are my slaves.” Thus it must be that there is one witness. This is sufficient to create the suspicion of kiddushin. And thus this is a difficulty against those who say that with one witness, we disregard her kiddushin.