This is a very common, classic group movement pathfinding problem, not exclusive to C3, and not an easy issue to solve.
A few options from simplest to most complex:
A. Use different targets to move to, don't move to the same place, at the same time.
B. Spread out upon reaching the destination, or triggered when in an undesirable state of overlapping.
C. Have units attempt to maintain relative distance by slowing down or speeding up while moving. This is a portion of flocking systems.
D. Implement full steering/flocking mechanics: gamedevelopment.tutsplus.com/series/understanding-steering-behaviors--gamedev-12732
E. All of the above.