If a latecomer enters while the Imam is bowing, should he pull the worshiper (who is already praying) to pray beside him, or should he wait until the Imam is heard, and then they both return (to the congregation)?

The matter is broad concerning the movement of the congregants to shift from the sides of the Imam to behind him after bowing. The congregant may pull him while he is bowing, or they may stand with him and then move back. It is sunnah (definition) for the Imam to move forward or for the two congregants to move backward if another congregant arrives, and this is permissible during standing or bowing. It is not sunnah in other positions, such as the final tashahhud (definition). If they stand beside the Imam during bowing or other parts of the prayer, their prayer is valid, especially if it is easier for them or prevents distraction.