In this drill the player throwing the rebound in, has the other two on its team to run back and forth distracting the other players. The player throwing the rebound in will throw it to its component. The component will run to their goal, blocking them.
Four players standing still make every ball handler's job harder. Teach V-cuts, L-cuts and back cuts so your team gets open and punishes defenders who overplay.
Good team defence is five players guarding the ball, not five separate one-on-ones. The shell drill is where that starts, so here is how to teach help-side positioning and rotations from the first week of the season.
Rebounding is the least glamorous thing in basketball and one of the most decisive. It is also almost entirely a habit, which means it is entirely coachable.