Hi,
If you know the actor to ignore you can use:
https://docs.unrealengine.com/latest/INT/Gameplay/HowTo/UseRaycasts/Blueprints/#singlelinetrace
else you can use
https://docs.unrealengine.com/latest/INT/Gameplay/HowTo/UseRaycasts/Blueprints/#multilinetrace
About visibility i don’t know.