Caiaphas was the son-in-law of Annas. He was appointed as high priest in 15 AD, serving under Pontius Pilate (26-36 AD) and thus also the one who held this office during the time of Jesus’ trial.
John may be Jonathan, son of Annas, who served as high priest after Caiaphas from 36-37 AD. It is possible that he was captain of the temple guard when the apostles were arrested.
No one knows for certain who Alexander was, but it is clear that the temple affairs were in the hands of a few powerful families.1
6 with Annas the high priest and Caiaphas and John and Alexander, and all who were of the high-priestly family.