Is Rezin,the king of Aram in Isaiah 7:1 confirmed by extra-biblical sources?
Yes we do. He is mentioned in Assyrian annals of Tiglath-Pileser III. Tiglath-Pileser III conquered Damascus and killed Rezin in 732 BC, annexing Aram (not Syria, although the geographic location of Aram was nearly the same as modern Syria). Here is what is found in the following reference: Lester L. Grabbe, Ancient Israel: What Do We Know and How Do We Know It? (New York: T&T Clark, 2007): p.134
In order to save his life, he (Raḫiānu, ie. Rezin) fled alone and entered the gate of his city [like] a mongoose. I [im]paled his foremost men alive while making (the people of) his land watch. For forty-five days I set up my camp [aro]und his city and confined him (there) like a bird in a cage. I cut down his plantations, […] …, (and) orchards, which were without number; I did not leave a single one (standing). I surrounded (and) captured [the city …]ḫādara, the ancestral home of Raḫiānu (Rezin) of the land Damascus, [the pl]ace where he was born. I carried off 800 people, with their possessions, their oxen, (and) their sheep and goats. I carried off 750 captives from the cities Kuruṣṣâ (and) Samāya, (as well as) 550 captives from the city Metuna. Like tell(s) after the Deluge, I destroyed 591 cities of 16 districts of the land Damascus. (RINAP 1, Tiglath-Pileser III 20, l. 8’-17’)
Notice here that Tiglath-Pileser tells us that he captured Damascus. In 2 Kings 16, it is recorded that the sack of Damascus by Tiglath Pileser was instigated by King Ahaz of Judah, ending in Rezin’s execution. Tiglath-Pileser does not mention his having executed Rezin, so we only have the Bible as a source for this, but given the amount of overlap between the biblical account and that of the annals of Tiglath-Pileser III, we can assume that this is true as well. This is part of the famous messianic prophecy that the Messiah will be born of a virgin, who will be called Immanuel (God with us).
As for Uzziah and Pekah, given the near-perfect correspondence between the account in Isaiah and the annals of Tiglath Pileser, will any honest person doubt that Uzziah and Pekah are real people? But just in case there was any doubt, Assyrian records say that king Uzziah (also known as Azariah) reigned over Judah for 42 years. 2 Chronicles 26 records his reign as lasting 52 years. Which is more likely to be correct? I believe that answer to this is obvious. There is also considerable archaeological support for the earthquake in the days of Uzziah (Amos 1:1), with data from Hazor, Gezer, Lachish and other cities showing an extreme destruction in 755 plus or minus about 10 years (Steven A. Austin, Gordon W. Franz, and Eric G. Frost, “Amos’s Earthquake: An Extraordinary Middle East Seismic Event of 750 B.C.” International Geology Review 42 (2000) 657-671.). You can assume without the possibility of error that Uzziah, Pekah and Rezin are real people who lived in Judah, Samaria and Aram in the middle of the eighth century BC.