The fact that "elders," in the vicinity of God's throne, is mentioned as early as Is. 24:23 would not support their assumption. And how is it that John addresses the elder as "lord" if he was his brother?
A well known dictionary had the following comment: As early as Is. 24:23 “elders” are
mentioned in connection with God’s enthronement. The fact that these are not
depicted in a judicial capacity does not rule out their judicial function. One
of the elders would act as godly spokesman and interpreter, while as a group
they would glorify God and proclaim His judgments (cf. Rev. 5:5; 7:13; 11:16-18):
The two passages Ex. 24 and Nu. 11 exerted considerable influence on other parts of the Bible and on Jewish exegesis. In obvious dependence on Ex. 24:9 f. the late apc. in Is., depicting world judgment and the manifestation of the coming kingdom of Yahweh on Zion and in Jerusalem, closes with the words: “And before his elders is glory,” Is. 24:23. The passage is a first example of the way in which apocalyptic likes to base its eschatological visions on sacred texts, so that it is itself to a large extent exegesis. In relation to Is. 24:23, Rev. 4 follows the same pattern in its vision of the 24 elders before the throne of God, → 668, 9 ff.
The 24 πρεσβύτεροι in Revelation. Special problems are raised by the passages in Rev. in which, in the visions of the divine, 24 elders surround the throne of God in heaven along with the four beasts, 4:4, 10; 5:6, 8, 11, 14; 7:11; 11:16; 14:3; 19:4. The thrones on which they sit (4:4; 11:16), the white robes and the crowns which adorn them (4:4), show that they are heavenly beings, and the title πρεσβύτεροι suggests that they are God’s council of elders (cf. Dan. 7:10). Yet there is no mention of God sitting in council with them nor do they seem to discharge a judicial office, cf. 20:4. Their function is not the exercising of their own dominion; it is simply adoration of the majesty of Him who sits on the throne (4:10; 19:4) and of the exalted Lamb (5:8–10) → θρόνος, III, 165, 21 ff. They sink to the ground, offer worship, and cast down their crowns before the throne of the eternal and omnipotent God (4:10) with songs of praise (4:11; 5:9 f.; 11:17 f.; 19:4 etc.). According to 5:8 they offer priestly ministry for the earthly community with harps and golden vials. Their divine service in heaven accompanies the events of redemption and judgment on earth, which the elders inaugurate and conclude with gesture and song. [1]
There is no suggestion that these elders are redeemed and transfigured men. They are plainly differentiated from the transfigured, 7 and 14. They are also distinguished from the angelic hosts (5:11; 7:11) which surround the throne and the four beasts. But they are so only as a higher class of angels which is closer to the throne of God than the others and which is entrusted in a peculiar way with His secrets. “One of the elders” functions as angelus interpres (5:5; 7:13) and the seer addresses him by the title of majesty, κύριος, 7:14.
[1] See Theological Dictionary of the New Testament, vol. VI, pp. 656, 668.