The seat cushions are easy. The seat backs are tougher but are not hard to do. All the side cushions are held on with studs mounted on the cushion backing wood. The studs go through oversize holes in the fiberglass coming down from the gunnel.
Reach up through the cup holder openings and you'll feel the stud with a nut and a couple of washers on it. It's easiest to use a self ratcheting box end wrench or a deep socket on a ratchet to remove the nuts. Look under the dash to check for studs below the windscreen.