Where to start with my project

So I’m struggling with this part. I think I understand the concept, where you basically make a separate event/BP that multiple different blueprints can call externally and then they can ‘speak’ to each other through that event.

However I’m simply struggling to figure out how to get the instances of the Runner (object moving along spline) to speak with the Spline they exist on, so I can make them both visible/hidden at the same time.

I’ve watched a number of videos, but I can’t seem to connect the dots between what they’re showing to what I’m trying to do. I’ve yet to find one which details about instances which aren’t in the outliner on begin play.