Who is 'them' in Jesus' prayer 'Father forgive them'?
Them refers primarily to the nation of Israel—the Jews—who bore chief responsibility for the crucifixion. Although Romans were involved, Scripture lays the onus on Israel, which should have known who Jesus was but did not. Jesus therefore asks the Father to forgive them.
Les explains that Romans and Jews were both involved in the crucifixion, but Scripture primarily lays the onus on the nation of Israel. Israel should have known, and could have known, who Jesus was because the Old Testament was full of it, yet Israel did not know. So when Jesus prays, 'Father, forgive them, for they know not what they do,' He is referring primarily to the Jew, not including the Romans as much.
Then said Jesus, Father, forgive them; for they know not what they do. And they parted his raiment, and cast lots.