Except for the “straight pullover” style, this is probably the simplest upholstered dining chair to do. It makes a great beginner project, if you are comfortable with a sewing machine. For each set of two chairs, you will need a yard of a plain fabric (or a yard and a half of patterned). You will also need tissue welting to make your piping.
Make a template using either the old fabric (you’ll have to remove the stitches to get just the top panel) or the plywood seat as your guide. If using the plywood, cut 1/2″ larger to accommodate the seam allowance. Measure each seat. Often, the “Captain’s Chair” seat is bigger!! Also, if you have a pattern, now is the time to make sure it is centered, and identical on every seat panel.