How i update a variable inside my widget blueprint from my blueprint actor and make it to work even if blueprint actor have more than one copy (instance) in the game?

[anonymous_user_2a687cc6]

I can make this working on my side as I have shown in above snapshots.
Make sure you are updating the DoorText in overlap event. You were doing Set Text in Event Construct of your widget which is called only once and setting the value one time. So you need to create a binding for your text in widget , not in event construct.