I don't think the Pathfinding behavior has that kind of 'choosing' functionality. One thing you can do is, after deciding which path you want to take but before starting the pathfinding, spawn an invisible solid on the other path so the path can't be chosen. Not ideal, but if no other object is meant to take those paths, it could work.
Another thing you can use is waypoints, and at the branch have the red guy choose between one waypoint or the other.
Here's a tutorial on it:
Here's one that's mostly just a capx: