Are these the same Bnei Nechar mentioned in verse 45?
Radak (Shmuel II, 22:46): No. These are the ones who do not obey me.
What is the meaning of "Yibolu"?
Rashi: They will weary. This is like "Navol Tibol" (Shemos 18:18); The Targum is Mil'ah Til'ah.
Rashi citing Menachem: They will become withered. This is like "Acharei Velosi" (Bereishis 18:12). He similarly explained "Navol Tibol" (Shemos 18:18).
Rashi: They will wither away. This is like "v'He'elah Navel" (Yirmeyah 8:13).
Malbim: [Nochrim who were far away] will weary [from the tedious journey to come to me to hear me].
What is the meaning of "v'Yachgeru"?
Rashi: They will fear. The Targum of "ume'Chadarim Eimah" (Devarim 32:25) is Chargas Mosa. Radak (Shmuel II, 22:46) - this is motion due to fear. Also Yonason translates so in Shmuel II 'vi'Yzu'un.'
Rashi citing Menachem: They will become soft.
Rashi citing Dunash: They will become Pise'ach (lame) due to the fetters on their legs.
Malbim: [Nochrim who were far away] will become lame [from the tedious journey to come to me].
What is "mi'Misgerosam"?
Rashi: Due to the harshness of the afflictions in their Masger (incarceration), that I afflict them.
Radak: They are closed in due to their fear. Even there, they will fear!
Radak (Shmuel II, 22:46, based on Targum Yonasan there): From their castles.
Malbim: [Nochrim who were] closed off in far away mountains [will toil to leave them, to come to hear me].