Catnip on the scratching posts is great, I have done that.

And double sided sticky tape on the the furniture and other places NOT to scratch also works great. I bought some mounting tape at the craft store last time, couldn't find the tape. It works fine.

If he is not scratching the furniture, what the heck is bothering your mom? The scent glands are NOT removed, so the cat can still leave her/his mark on the scratching post as 'owned' territory.

I have one cat with front paws declawed - her first owner did that when she was a kitten (I am her third owner! first oe died; second moved into elderly housing where only 1 cat was permitted, and she had 2.) Her front paws look so strange compared to the other cats here. She still jumps and climbs on the bed, sofa, and cat perches here. She is a bit less stable in her antics because she can't hold on. Her paws are short and awkward looking.

Good luck talking your mom OUT of the horrible idea.