If you read the KJV, they are identified as Christians who have been chosen to reign with the Lord during the thousand year kingdom.
Revelation 5:9-10
9 And they sung a new song, saying, Thou art worthy to take the book, and to open the seals thereof: for thou wast slain, and hast redeemed us to God by thy blood out of every kindred, and tongue, and people, and nation;
10 And hast made us unto our God kings and priests: and we shall reign on the earth.
As for the apostles, I believe you will find Judas was replaced by Matthias in Acts 1.