Both hands are BP_MotionController actors and has Hand variable enum, Left or Right value. But maybe you are implementing in complicated way, easier is if you create “touchable” class BP. In BP_MotionCotroller is already done (in the VR Template) the RumbleController event for vibrate them , if you want specific haptic effect check if the hitted or overlapped component/object play your desired effect.
If you created the VR Template you have it already in BP_motionController, at least the vibration at grab per hand. If you need more info just reply, help you when have more time free.