1)
From Oved Edom came 13 Mishmaros. Did all guard in the south, which has only four gates?
2)
What do we learn from "ul'Vanav Beis ha'Asufim [Shenayim Shenayim]"?
1.
Redak: It was a house outside the Azarah, in the south.
2.
Radak citing Tamid 27a #1: There were two guards for each of the two Asufim.
3.
Radak citing Tamid 27a #2: There were two guards for the two Asufim - one for each.
4.
Malbim: For his six grandsons, the lottery fixed that four will guard in Beis ha'Asufim, and the other two in Shupim (the start of the coming verse).


