1. It seems that the first case is too straightforward to be the subject of a dispute. This is because in the Reisha d'Reisha there are "Tarti l'Teivusa" -- there are two advantages: (a) the wine belongs to the Yisrael, and (b) the Yisrael lives in the courtyard. These two advantages are not present in any of the other parts of the Beraisa, because in all other parts either the wine belongs to the Nochri, or the Yisrael does not live in the Chatzer. Since there are Tarti l'Teivusa, even if the Yisrael does not possess the key or the Chosam, it is obvious according to everyone that the Nochri is afraid to touch the wine.

2. In addition, I found in the Sefer Chemdah Genuzah Teshuvas ha'Ge'onim #116 (this Sefer, published in Yerushalayim in 5623 with a Haskamah from Rav Meir Auerbach, the author of Imrei Binah, is a collection of manuscripts ascribed to the Ge'onim, and the Teshuvah cited herein is ascribed to Rav Tzemach Ga'on) that the Tana accepted what Rebbi Yochanan said to him, that if the Yisrael lives in the same courtyard the wine is permitted even if the key and Chosam are not in his hands. Consequently, this statement of Rebbi Yochanan is accepted as Halachah. It follows that in the first part of the Beraisa, even if the key and Chosam are not in his hands, nevertheless since the wine belongs to the Yisrael and he also lives in the Chatzer, the Halachah is that it is permitted, and if the Chachamim would have disagreed with this, the Halachah would not be such.

Yeyasher Kochacha,

Dovid Bloom