The Rocket Brothers are a family of Team Rocket Grunts. They are among the 30 Team Rocket Grunts who infiltrate Silph Co. in GenerationsI and III. Prior to battling, each brother declares himself as one of the four Rocket Brothers. Afterwards, the brother will warn the player that his brothers will avenge him, even if the player has already defeated the other three brothers. Defeating all four Rocket Brothers (or not defeating them, or else only defeating some) has no bearing whatsoever on the storyline. Moreover, the Rocket Brothers are never seen again after Team Rocket is cleared out of Silph Co.
The Rocket Sisters are a family of Team Rocket Grunts. They are among the 30 Team Rocket Grunts who infiltrate Silph Co. in Generation VII [[Let's GO. They replace the Rocket Brothers from GenerationsI and III. Prior to battling, each sister declares himself as one of the four Rocket Sisters. Afterwards, the sister will warn the player that his brothers will avenge him, even if the player has already defeated the other three. All interactions with the Rocket Sisters do not affect the plot, and they are only seen during the Rocket attack on Silph Co.