1)
What are "Amim" and "Le'umim"?
1.
Radak: They are families of Yisrael, like "Amim Har Yikra'u" (Devarim 33:19), and "Acharecha Vinyamin ba'Amamecha" (Shoftim 5:14).
2.
Malbim (67:3, Bi'urei Milos): Amim are esteemed collections [of people], with a king over them. Le'umim are Umos with a common creed.
2)
Why does it say both "Odecha va'Amim" and "Azamercha ba'Le'umim"?
1.
Radak: The matter is repeated in different words, like is common.
2.
Malbim: Odeh is thanking for the good. Zemer is singing His praise; that is among Le'umim, who have a creed. I will tell them Hashem's praise, that He is greater than all Elokim.
