Hi.
Use this answer to get a reference for your sedan inside the Widget blueprint: https://answers.unrealengine.com/questions/363020/stuck-trying-to-display-a-variable-to-the-players.html
Is the second image, but instead of “ThirdPersonCharacter”, you cast to “Sedan”.
On Your Sedan blueprint, create Two CustomEvents “Handbrake On” Handbrake Off" and connect than to the SetHandbrakeInput nodes.
When you on the button, call from the “Playerdata” variable the event “Handbrake On”, when release “Handbrake Off”.
I hope this help you.