The high priest "rose up" (Gr. anastas, cf. Acts 5:34) taking official action as leader of the Sanhedrin. As mentioned above, the high priest and most of the Sanhedrin members were Sadducees ( Acts 4:1). The Holy Spirit filled the believers, Satan had filled Ananias and Sapphira, and now jealousy filled the Sanhedrin members, particularly the Sadducees. They had the apostles arrested and confined in a common (public) jail (Gr. teresis demosia). [source][source][source]
"The Sadducees are often seen as more hostile to the new movement than the Pharisees in Acts , whereas in Luke"s Gospel the Pharisees are major opponents of Jesus. This fits the shift of attention to Jerusalem from the setting of Jesus"s ministry outside the city. The Sadducees have more to lose, since they control the council and have worked out a compromise with the Romans to share power." [1][source]
"Sadduceeism is rampant, so is Pharisaism; they are represented to-day by rationalism and ritualism. These are the opponents of living, vital Christianity to-day, just as they were in Jerusalem." [2][source]
"It is amazing how much envy can be hidden under the disguise of "defending the faith."" [3][source]
Peter and John have been the apostles in view to this point, but now we read that Peter and the apostles (plural) stood before the Sanhedrin ( Acts 5:29). It is probable, therefore, that more apostles than just Peter and John are in view in this whole incident beginning with Acts 5:17. [source][source][source]