After a thorough clean the whole car looks much fresher.
Not sure about getting it back in yet; there looks to be some form of spring loading which might make things difficult
Replacing the rear seats is quite simple when you know the knack:
Move the seat fully back on its runners. Make sure the release bar is lifted and the spring loaded catches (underneath at the back) have clicked so the springs extend over the balls (you will see what I mean when you look)
Lower the seat into place and locate the catches in the rear holes - do NOT press home at this stage as the seat will feel rocky.
Through the sliding door, you will find the inboard mounting might be pushed into place right away - DON'T - locate and secure the spring loaded outboard bracket (nearest the camera) first.
The outboard mounting (nearest the outside of the car) is spring loaded through a gas damper - carefully lever the mounting down (stout screwdriver) whilst at the same time keeping the seat slightly airborne. If you don't keep it clear of the bodywork you will bend a bracket and make life very difficult (see below).
Having compressed the gas damper you should find the mounting somewhere near the stud - drop the nut on loosely.
Rotate and locate the inboard mounting - drop the nut on loosely - the seat is now located in position.
From the back, firmly press both sides of the seat until you hear the locks click into place.
Finally tighten the nuts; reconnect the connectors and refit the covers.
. . . . and not bent at 90° like this one.
Takes about a minute to put a seat in if all goes well - over an hour if you bend the bracket without realising. Please don't ask me how I know this!