What is the meaning of "Im Acheichem"?
Rashi #1: It is with Bnei Gad and Bnei Reuven. 1
Rashi #2: It is with your brothers who remained to guard the cities [in Ever ha'Yarden] with the women and children. Also they received a share of the spoils.
Radak: If he addressed Gad, Reuven and Chetzi Menasheh, he told them to divide the spoils with the Shevatim in Eretz Yisrael proper, before returning.
Malbim: The spoils were divided among the Shevatim. Chetzi Menasheh in Ever ha'Yarden needed to divide with the half in Eretz Yisrael proper.
Radak: This is if he was speaking only to Chetzi Menasheh.
QUESTIONS ON RASHI
Rashi writes that they must divide with the men who remained to guard the cities [in Ever ha'Yarden]. They left only women and children!
Malbim: Only about 40,000 crossed the Yarden to fight (4:13), only about a third of the men of these tribes counted in Parshas Pinchas. 1
Why did Radak leave this question difficult? Even if the reason they stayed was not in order to guard the cities (Pele Yo'etz (Bore'ach) says that Aveiros disqualify even from fighting in a war of a Mitzvah), surely now that they stayed, they guarded! Perhaps he holds that after Teshuvah, they all crossed the Yarden to fight. Or, perhaps we share spoils with Shomrei ha'Kelim (Rambam, Hilchos Melachim 4:9) only if they were proper to fight. So implies Mishnas Ya'avetz (Zolty) Shemitah v'Yovel 13:12. - PF)