Mark out a small area, typically 1/3 of the court (depends on group size).
Select someone to be the tagger. All the playes in the group have balls and on the coach's call start to dribble around the area.
On the coach's second call the tagger starts to dribble with their ball after the other members of the group, trying to tag them. If they successfully tag someone then they now become the tagger.
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.
Good spacing is only the start. The best modern offences teach players to attack the defence's rotations and play in a permanent 4-on-3 - here is how to coach that read.
The ball screen produces almost half of all professional offensive possessions, yet most teams still teach it as a memorised play. The modern approach trains the read - giving players a framework to decide based on what the defence does, not what the coach called.