Hi Henry,
I saw a man from the RAC do this on my car many years ago when he disabled an RAC Tracker that was faulty (that’s where the RAC place trackers, under the rear seats).
To get the seat backs off he pressed the top of the seat down whilst pulling it out at the same time. It seemed as if it was just metal spring clips holding it in place. It did seem that a lot of pressure was required.
You may need to talk to one of the specialists just to confirm this before you damage anything. I have also asked a friend who may have removed his seats in the past for advice.
Graham