If you are using blueprints, I would recommend using the Box Overlap Actors node (see documentation: Box Overlap Actors | Unreal Engine Documentation). If not, check the implementation of that node in C++ and see how it’s implemented and do the same thing (I’m at work right now so I can’t give you any more details without checking up the implementation. But it most certain uses the collision query functions in UWorld). This is basically the same thing as eXi says, a “multi box trace”.
This would use the collision octree to make sure that you query a minimal amount of actors within the engines collision system.