There are many ways to do it. You can use an invisible RoomZone sprite. When the player collides with it, close all doors connected to this RoomZone. For example:
Player on collision with RoomZone
RoomZone is overlapping Door
.. Door set animation to "Closed"
Or instead of overlapping check you can add doors to a hierarchy and pick Door instances which are children to RoomZone.
When the player kills a monster, pick all remaining monsters overlapping RoomZone and if there are none, open the doors.