‘But when they had commanded them to go aside out of the council, they conferred among themselves, saying, “What shall we do to these men? for that indeed a notable miracle has been wrought through them, is openly known to all who dwell in Jerusalem; and we cannot deny it. But that it spread no further among the people, let us threaten them, that they speak henceforth to no man in this name.” '
So having heard the case they put the accused outside the room while they discussed what they would do. What happened there may well have been communicated to the Apostles by one of the members of the Sanhedrin such as Nicodemus or Joseph of Arimathea. Or other members of the court may have passed on the information, either deliberately, or accidentally through their servants overhearing what they said to heir wives.
They then discussed what they should do with these men. They admitted that a notable miracle had occurred. It could hardly be denied. Everyone was talking about it. So their conclusion was that the miracle could be quietly forgotten and that they should simply give the men an official admonishment, commanding them no longer to do things in the name of Jesus under pain of punishment (usually by beating). What mattered after all was to prevent the teaching from spreading.
Here then is the pivotal point of the whole chapter, the attitude taken towards the Name of Jesus both by these men and by the Apostles. The Sanhedrin rejected it and forbade its use. The Apostles determined that they would use every means to proclaim it, because there was salvation in no other. The same choice faces us all today.