Notes on the Bible, by Albert Barnes, , at sacred-texts.com
The daughters of Zelophehad had obtained an ordinance Num 28:6-11 which permitted the daughters of an Israelite dying without male issue to inherit their father's property. The chiefs of the Machirites, of whom Zelophehad had been one, now obtain a supplemental enactment, directing that heiresses should marry within their own tribe.
Be taken away - i. e. be permanently taken away. The jubilee year, by not restoring the estate to the tribe to which it originally belonged, would in effect confirm the alienation.
Unto their father's brothers' sons - Or more generally, "unto the sons of their kinsmen."