Although the Gemara refers to dinei mamanos [financial matters], some Rishonim raise the following concern regarding gittin and kiddushin as well: If there are relatives present at the giving of the get or at the kiddushin, then should we say that all eidim who witnessed the ceremony are disqualified, in accordance with the principle “if one of them is found to be a relative or is otherwise disqualified, their entire testimony is voided”?
Tosfos (Makkos 6a, d.h. Shmuel; see also Rosh 1:11) explains that since the Gemara only applies this rule to witnesses who come to testify in beis din, and not to those who merely witnessed the action, it would not apply to those who witnessed the kiddushin.
The Ritva, (Kiddushin 43a, d.h. Itmar) disagrees. He explains that when the Gemara differentiated between witnesses who come to testify in beis din and those who saw the act, “that referred to monetary and criminal cases, regarding which the testimony is not fulfilled until the witnesses come to beis din... However, for kiddushin, regarding which the testimony does not only come to confirm the act, as even if we know that she was mekudeshes [betrothed], the kiddushin is not valid without testimony... if invalid witnesses join them during the kiddushin, the entire testimony is disqualified.” In other words, the testimony for kiddushin is fundamentally a different type of testimony. It is not to verify that the kiddushin occurred, but rather, “edus lekiyum hadavar,” and therefore, as we mentioned above, if the kiddushin is performed without witnesses, it is not valid.
Although the Ritva does not accept this view, he records that the practice of his rebbe was that “whenever there are valid and invalid witnesses at the (kiddushin) ceremony, it is necessary to designate the eidei kiddushin (i.e. the witnesses for the kiddushin), because if not, since there is an invalid witness among them, the testimony of all of them is disqualified.” By designating witnesses to the exclusion of others, the “kat” of eidim, which does not include disqualified witnesses, is defined.
