I have made slipcovers and reupholstered furniture. Those chairs would be easier to reupholster then make covers for them. They are in bad enough shape that it would show through the covers. The covers that are on them are probably stapled in place. Take the staples out, remove the old covering and use them for a guide to make the new covering. It really isn't that hard to do if you take your time and pay attention as you are removing the old covers...Wish I could be there to show you.....
Ditter