“who among them has declared these things.” Here in Isaiah 48:14, the “them” in the phrase, “who among them,” refers to the pagan gods, the idols. Who among the idols has been able to declare the future like Yahweh can? None of them. The contrast and contest between Yahweh and idols is the whole subject even from Isa. 48:1, and the idols are specifically mentioned in Isa. 48:5: “I [Yahweh] showed them [future things] to you, lest you should say, ‘My idol has done them, and my carved image and my cast image have commanded them.’”
“He whom Yahweh loves will perform his pleasure on Babylon.” The text does not tell us who the “He” is in this verse, but the context and scope of Scripture tells us, and it is Cyrus the Persian (cp. Keil and Delitzsch, Commentary on the Old Testament). Some scholars say it is Judah itself, but Judah does not fulfill the prophecy here in Isa. 48:14-16.
Cyrus arose from a lesser status to conquer many kingdoms and rule over the largest kingdom the world had ever seen by that time. But he did not achieve that status on his own. God raised up Cyrus, called him by name, gave him a title of honor, gave him holy spirit, and empowered him (Isa. 45:1-6). We know God gave Cyrus the gift of holy spirit to empower him because that is the meaning of God’s calling Cyrus “His anointed” in Isaiah 45:1, and that is confirmed in Isaiah 48:16.
Isaiah 45:1-6 tells us that God raised up Cyrus for the sake of Israel and Judah. So it was that Cyrus did “perform God’s pleasure on Babylon” by conquering it, and it was Cyrus who, in the first year after that conquest allowed the people of Israel to return to Judah from the Babylonian captivity (cp. Ezra 1:1-8).