Still a little trouble understanding, but I’ll try my best. In reading this now, I don’t think you need an interface.
I would not do this in two blueprints. I would put both objects into a single blueprint, allowing them to be moved independently of each other. This will make it much easier for both objects to communicate with each other. You can make it so two blueprints communicate with each other, but it’s messier and I wouldn’t do it unless I had to.
You can have 2 meshes and 2 collision boxes (one per mesh, a child to the mesh). You would have a pretty much identical event for each collision box (or rather, pressing F inside each collision box).
Player presses F inside collision box 1 – > Set Variable 1 = Variable 2 – > Set Variable 2 = 0
Edit: If you really need to have each object in its own blueprint, let me know and I can help. I did this with a teleporter system where I needed to make sure I could link any number of teleporter pads together.
I need to put them in 2 blueprints because the second blueprint is suppose to communicate with more blueprints and not just that one. (btw it’s a variable i made in the character blueprint)