The seats are affixed by a pivot/slide arrangement - the front pivots, the rear slides. The ratchet mechanism is on the outboard rear of the seat; the pawl is inboard of the slide.
It's unusual for the pawl to be hanging up; what is more common is the front pivots rust into immobilization. Pull up the front carpets where the seat posts meet the floor; spray some penetrating oil there. After letting them sit overnight, some rocking back and forth in the seat may work it loose.
Be advised this area of the floorpan is a weak spot on Mantas/Asconas - I've had Mantas where the front pivot area rotted so bad the seat posts dropped thru the floorpan! This may be the case here - hard to move seats are a sign rust has been at work on the floor.