You can get tiny--yes tiny--claw sheathes on amazon if you haven't considered this optoin. We used them to train a cat out of climbing on the couch when I lived at home.

They're tiny, soft rubberish, and wear off of their own accord in about two weeks to a month (depending on cat activity), but that's generally enough time for the cat to forgo all fabric, since it doesn't affect their ability to cling to solid surfaces or jump around safely, just--poke holes in your brand new couch or climb curtains (and on occasion, fail). But in your case, if the scratching could be serious or hurt the other cat, it would act as a blunter.

They are not easy to get on--you put one on each tiny claw--but two people can do it. By observation, it made them slightly more clumsy until they adapted with hard surfaces (about two hours of hilarity then back to normal cat) but fabric and flesh were safe. Honestly, they seemed to forget they even had them on by end of day.

(Forgive me if you know about these or have used them. A surprising number of friends had never heard of them and were thrilled with an alternative to their current methods to teach the cat not to destroy furniture or hostility toward their new dog.)