1)
What are "Anshei ha'Matzevah"?
1.
Radak: This is like Matzav Pelishtim (army officers), like I explained above (13:23).
2.
Radak citing Targum Yonasan: They are Netzivim around the camp to guard it.
2)
What is the significance of the words "Alu Aleinu"?
1.
Malbim: This shows that their strength departed in front of Yonason.