Commentary for Kiddushin 101:13
ה"ד אילימא דאמר כולכם קני את וחמור הוא ואת וחמור לא קנה
This implies, [if he betroths] one of a woman and her daughter or of a woman and her sister [without specifying which], she is betrothed: yet why, seeing that it is kiddushin which may not be followed by intercourse? Hence this refutes Raba! - Raba can answer you: Yet even on your view, consider the second clause: AND IT ONCE HAPPENED TO FIVE WOMEN, AMONGST WHOM WERE TWO SISTERS, THAT A MAN GATHERED A BASKET OF FIGS, WHICH WAS THEIRS, AND WHICH WAS OF THE SEVENTH YEAR, AND HE DECLARED, 'BEHOLD, YE ARE ALL BETROTHED UNTO ME WITH THIS BASKET, AND ONE ACCEPTED IT ON BEHALF OF ALL: THE SAGES THEN RULED, THE SISTERS ARE NOT BETROTHED. Thus, it is only the sisters who are not betrothed, but the strangers are. Now how is it meant? Shall we say that he declared: 'All of you'<span class="x" onmousemove="('comment',' I.e., 'All of you be betrothed to me'.');"><sup>20</sup></span> - it is a case of 'you and the ass acquire', and such does not acquire.<span class="x" onmousemove="('comment',' If one bestows gifts upon a living person and an unborn child simultaneously, not even the first acquires his gift, because the second cannot, - metaphorically, 'you and the ass acquire them'. Hence here too, since the sisters cannot acquire aught thereof as kiddushin, the others cannot either.');"><sup>21</sup></span>
Daf Shevui to Kiddushin
So what exactly did he say? If he said “all of you” then this would be like a case of a person who says to another person and a donkey (or any animal), “You and the donkey should acquire this.” Since the donkey cannot acquire, the other person does not either. So too here, since the sisters do not acquire the betrothal money, neither would the non-sisters.
Rather, he must have said, “one of you [is betrothed to me].” The sisters are not betrothed because this is “kiddushin that cannot be followed by intercourse” since he could not have sex with either one of them.
This discussion continues tomorrow.