Regarding the 24 elders, what is the exegetical significance of preferring the reading τω θεω ημας over the reading τω θεω in Rev 5:9?

Most English translations in Rev 5:9 read something like "You purchased people for God by your blood from every tribe and language and people and nation." However, the Revelation ECM/CBGM data prefers the reading τῷ θεῷ ἡμᾶς over the reading of τῷ θεῷ (supported by only one Greek manuscript, 02). If I am not mistaken, this would read something like "you purchased ***us*** for God by your blood...". My question(s) pertain to the significance of this change in reading. Who are the 24 elders? How does this reading change our understanding of their identity and function? Are they a part of the redeemed?