Here, try this. If you create you Door BP with the collision box built in, then possess the pawn on overlap of the collision box, you solve all of these issues. I had it possess and then unpossess after a delay. It was working fine. There are some errors that occurred with controller input not being able to access the original player character during the time it was unpossessed which was not fixed with “disable input”. Might just be the order of execution, I am sure you can figure it out with some trial and error. But as for the main issue of switching the camera back and forth this def. works, you wil just need to add your extra script for being able to control the camera through the newly possessed pawn. Hope this helps!
