A corner that's theirs.
Every cat needs somewhere of its own to tear at.
The scratching was never the problem - it's instinct, the way a cat stretches long, marks its ground and keeps its claws honest. The trouble is only ever where it lands. Give that urge a surface of its own and the sofa stops bearing the weight of it; fix it where they already gather, lift it away when you don't, move it as their habits shift. A small thing on the wall, and the home feels a little more shared - theirs, as much as yours.