I am making a 2D top-down game and I am looking for some help in regards to the collision resolution between two moving (circular) objects.

Basically, what I am trying to achieve is the effect of large groups of enemies which "cluster" behind one another naturally rather than moving through or on top of each other. I'm not looking for anything sophisticated like boids or actual grouping mechanics-- just enough to make it so enemies collide properly.

Using a bounding circle approximation is accurate enough for my purposes, and so actually detecting a collision is simple. What I need is to only allow the objects to move far enough until there is a collision and then stop.

Thank you for any help or assistance you have.