"And I saw thrones, and they sat upon them, and judgment was given unto them: and I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years." - Revelation 20:4 KJV
a) John saw thrones.
b) "They" sat on the thrones to judge
c) AND John saw the souls of beheaded martyrs
d) AND John saw the souls of those that had not worshipped the beast
It COULD be the case that b, c, & d are descriptions of the same people. It could ALSO be the case that b, c, & d are separate descriptions of separate groups of people. It could ALSO be the case that b, c, & d descriptions apply in varying degrees to each individual.
It is NOT necessarily the case that all of those on thrones are beheaded.