If I were you, I’d have a single background rendered of the interior of two rooms from a suitable angle and have my characters spotted where I want them in their respective rooms either doing their animations or have them do custom poses using overlays and the (blurred) wall that divides them as separate overlay that goes on top, above the the characters scenes while I use the zooms and pans to “transition” from one room/zone to the other.
You could also do the same thing using the two background render as an overlay instead of a background and shift it to have the same effect, but you’d need to animated the wall and have the walks to command for the characters unless you make the character overlays too in which case you’d also use shift.
If you mean like the post above, then you’d just have a background, then characters on top, then an overlay of a wall set to opacity 1 and have the character eavesdropping at the top layer (on top of the wall). After that, you can move the character to the side slowly with the walks to spot command (so that they’re not obscuring the reader’s view and have the wall overlay fade at the same time within however many seconds you want to reveal the characters in the room.