1)
Why does it specify island residents?
1.
Radak: Because Tzor was an island, it says that the other island residents will be astounded.
2.
Malbim: This is like it says above "Yechredu ha'Iyin Yom Mapaltech" (26:18).
2)
What is the meaning of "u'Malcheihem Sa'aru Sa'ar"?
1.
Radak: They will fear lest happen to them like happened to you. Sa'ar is agitation; it is the same with a Sin or Samech. Malbim ? this was internal. Externally, their faces were angry [amidst fear lest also other islands be broken].
3)
What is the meaning of "Ra'amu Panim"?
1.
Rashi: They are angry faces. Likewise, "Ba'avur Hare'imah" (Shmuel I, 1:6). The Targum of Telunah is always Tur'amasa (e.g. Shemos 16:7).