1)
Why will they be ashamed?
1.
Radak: They be ashamed of their Gevurah and hope (their Gevurah did not help them, and their hope was fulfilled - PF. Refer to 35:4:3:1.)
2)
What is the meaning of "Yisogu Achor"?
1.
Radak: They will turn back. The same applies to "Lo Nasog Achor Libenu" (44:19). When You come to greet them with a sword and spear, they will turn away from pursuing me.
3)
Why does it say "v'Yachperu Choshevei Ra'asi"?
1.
Radak: They will be ashamed that they wanted to harm, and they could not.
2.
Malbim: ("Choshevei Ra'asi" merely want to harm me.) They are lighter than "Mevakshei Nafshi" [who wanted to kill me; the latter will be more ashamed].