Here all instances of "they" and "them" refer to the Jewish leaders in Rome. All instances of "him," "his," and "He" refer to Paul ([Acts 28:17](../28/17.md)).
Here "kingdom of God" stands for God's rule as king. Alternate translation: "told them about God's rule as king" or "told them how God would show himself as king" (See: [[rc://en/ta/man/translate/figs-metonymy]])