Hello. Thank you for asking your question on just answer. My name isXXXXX will try to help.
It is going to be tough to get them to stop completely.
You can try putting double sided sticky tape on the spots they like to scratch. Cats do not like their paws sticking to things.
Alternatively, you can put aluminum foil on the scratching areas. Cats do not like foil.
You could try taping balloons there as well.
You can try booby trapping the chair with a soda can filled with coins. When they scratch, the can of coins falls and makes a loud noise.
I think, if they are destroying the chair, I would put "soft paws" or "soft claws" on them. They are little rubber nail caps. You have to change them every 3-4 weeks but they can not do much damage with them on.
You can try a "scat mat" too. It gives a little shock when they cat steps on it so you would put it by the chair. I have used it and it works well.
You will also want to get a scratching post so the cats have an upright place they are allowed to scratch. You can get a commercial made one or I have even used a log upright. Rub cat nip all over it. Have multiple scratching posts where they are allowed to scratch.
I hope this helps.