(Mishnah): If the Pesachim of Reuven and Shimon became mixed [each is Memaneh an outsider...]

Suggestion: Our Mishnah is unlike R. Yehudah:

(Beraisa - R. Yehudah): "V'Im Yim'at ha'Bayis mi'Hyos mi'Seh" - this teaches that a Chaburah may diminish (people may withdraw from it) as long as one of them (the original owners) remains. (Here, perhaps the one original owner of each Korban withdraws from it!)

R. Yosi permits, as long as Pesach is not left without owners.

Rejection (R. Yochanan): It is even like R. Yehudah:

R. Yehudah forbids slaughtering Pesach for an individual - therefore, from the beginning Reuven [or Shimon] is not considered the sole owner, since he must Memaneh others with himself.

Support (Rav Ashi - Mishnah): The same applies to five Chaburos, each with five members...

It would not suffice it one of the five Chaburos had only four members, for then they cannot ensure that one of them will remain on their Pesach!

(Mishnah): On Erev Pesach, from shortly [half an hour] before [the time of] Minchah [Ketanah, which is at nine and a half hours of the day], one may not eat until dark;

Even the poorest Yisrael may not eat until he reclines [like a free man], and they (distributors of Tzedakah) should not give to him less than four cups of wine, and even if he is supported from the Tamchuy (food given daily to the poorest people, if they did not give him, he must strive to obtain them).

(Gemara) Question: Why does the Mishnah specify Erev Pesach - the same applies to any Erev Shabbos or Erev Yom Tov!

(Beraisa #1 - R. Yehudah): On Erev Shabbos or Erev Yom Tov one may not eat after Minchah, in order that he will enter Shabbos [or Yom Tov] with appetite.

R. Yosi says, he may eat until dark.

Answer #1 (Rav Huna): Our Mishnah is R. Yosi, who permits eating on any other Erev Shabbos or Yom Tov until dark;

He agrees that this is forbidden on Erev Pesach, to enable one to eat Matzah with appetite.

Answer #2 (Rav Papa): It is even like R. Yehudah - on any other Erev Shabbos or Yom Tov after Minchah is forbidden, but shortly beforehand is permitted;

On Erev Pesach even shortly beforehand is forbidden.

Question: Also on Erev Shabbos shortly before Minchah is forbidden!

(Beraisa #2 - R. Yehudah): On Erev Shabbos one may not eat after nine hours of the day, in order that he will enter Shabbos with appetite.

R. Yosi says, he may eat until dark. (We do not say that the Beraisos contradict each other - in Beraisa #1, 'after Minchah' could mean from shortly before Minchah.)