Hm, i just thought about using a box that you scale and position with your mouse clicks. After you release the mouse button again, you activate the collision for that box and get the actors inside…
But maybe a simple box trace, like i posted you above, from start point (mouse click) to end point (mouse release) would be enough. That’s the easiest thing to do and won’t hurt your game performance.
Maybe you will need to use a “multi box trace” instead of single one.