One very common problem with Pathfinding behavior is preventing pathfinding objects from colliding and overlapping each other. There are many different methods and ways to approach this, unfortunately, none of them are easy or 100% working. I have two demos, which are also far from perfect, but may be a starting point for someone making an RTS game.
PATHFINDING
C3P C3P Prevent pathfinding objects from colliding with each other. Two versions: Avoid overlapping while moving + Avoid overlapping at the target point.
C3P And as a bonus - accurate Pathfinding. You may have noticed that pathfinding objects almost never stop at the exact target point, sometimes they stop early, sometimes late, sometimes miss it completely. This example provides a solution.