Have you thought about using cat tip covers. We had to get them after we got a new couch and they had destroyed the last one(arseholes indeed!). Sorry to hear about your sheets :(
That's why there's cat nail covers! http://imgur.com/2lnd1Vk
Edit: noticed I'm getting some downvotes, I assume because you all want a link for where you can buy it
Edit 2: still seeing some downvoting, I assume because the price was too steep, so here it is for 70 cents cheaper at amazon
NAH, can't give one to you as getting rid of the cats is a decent option, also not giving one to parents as they have a right to an undamaged home. Not gonna comment on declawing as an option, I'm really torn on that one.
There are other options, we've tried Claw caps before with persistent, untrainable cats (https://www.amazon.com/Soft-Claws-Cats-System-Medium/dp/B00074W45S/ref=sr_1_5?dchild=1&keywords=Cat+Claw+Caps&qid=1623333915&sr=8-5) for example....
Try Soft Claws:
Soft Claws for Cats - CLS
https://www.amazon.com/dp/B00074W45S/ref=cm_sw_r_awdo_5CPBDGA81WS7DQ7XTN13
You might have to get soft paws to cover her nails. They glue on and last from 2-4 weeks. Get pink ones and your kitty will look fabulous. You will probably need help putting them on. You should also use nail clippers and trim her nails every 2 weeks. Don't go too far though, avoid the 'quick' (darker color) in the claws.
http://www.amazon.com/gp/product/B00074W45S/
Also, my cat didnt like his first few scratching posts because they werent sturdy enough. Cat's need their scratching post to be very sturdy and not move, and it should also be in an area she frequents, not off in a back corner somewhere. Get one with a perch so she can see a great view of the house in all directions and she will use it a lot. Now that I got a full sized cat tree he scratches the hell out of it. Don't even bother with the small ones, you're going to have to pay a bit more, but she will love it. Get one that has Sisal AND carpet posts to scratch.
http://www.amazon.com/Go-Pet-Club-Furniture-Beige/dp/B005R46A6W/
http://www.amazon.com/Best-Choice-Products-Scratcher-Furniture/dp/B00NWJDSKK
I also discipline my cat by making a 'SSSSSSSSSSSSSS' noise and he knows now that means he needs to stop what he's doing. Works better than yelling NO, and he knows that sound is just for him. Of course then I sound like a hissing weirdo, but whatever. I've heard its an innate behavior of cats to respond more to the S sound. I've also heard that that's the same reason cats should have an S sound in their name and they will learn it better.