If the seats are tight to the rails and the floor you possibly have a bolt or bolts loose that hold the seats to backs. On the door side of both seats is a mechanism for tilting or reclining the seats, it attaches to the seat frame with two hex head bolts, it attaches to the seat back with two Torx head bolts, (most are T45). any of these bolts could be loose.
On the inboard side is a single Torx head bolt that holds that side to the seat frame.
If either of the seat back bolts are loose, you will need to remove the pad that covers the frame. To do this, tilt the seat back forward as far as it will go and gently pry the interlocking plastic strips apart on one end and just slide a screw driver between them to the other end. Next slide your HAND up between the back of the seat frame under the material and locate the clip that has the odd material and plastic clip attached to the end of it and pull it over the lip it locks over. Now the sides of the frame has sharp edges that grab everything, (your skin especially) slide the back pad up off of the frame far enough to tighten the bolts. (when the material won't move up anymore check the sides where the foam is hung up on a sharp corner). It all goes back together the opposite of how it came apart.
As a note, if your seat backs are broken, you can use any Ford Ranger/Explorer seat frame or back frame that is the same style you presently have. So all you will care about is whether the frame is in good condition or not, the material can be shot, that will make it easier to get the material off anyway, SHARP KNIFE OR SCISSORS. If you find a seat at a wrecking yard, get the material of of right there to make sure you are getting a good frame and the right one.