Any extreme, unusual behavior in cats should be taken as a sign of health problems. They can't tell you when they aren't feeling well, so they have to show you. If the cat checks out ok at the vets, then investigate whether anything new has been added to the furniture, people, or things. Could be a statement of extreme dislike!
You put catnip on the cat furniture.
If dogs suddenly had cat ears, it would likely not have a significant impact on their behavior or abilities. Dogs primarily rely on their sense of smell and hearing, so the addition of cat ears would not drastically change their sensory capabilities. It would simply be a physical change in appearance without much functional difference.
To prevent your cat from scratching furniture, provide a cat claw post near the furniture, encourage your cat to use it with treats or catnip, and regularly trim your cat's claws to reduce scratching.
Male cat's spray but a female cat will urinate on furniture. If you get them fixed they won't spray. Make sure their litter box is clean. Spray your furniture with orange or lemon scent cat's can't stand that scent.
The feral cat has either decided to trust you, OR the cat is sick. A cat will often isolate, stay in one place, and even hide when in pain or ill.
that means your cat is smart
The cat suddenly went silent after meowing because it may have been startled or sensed danger.
To prevent your cat from scratching furniture, provide a cat scratching post and nail file for them to use. Encourage your cat to use the scratching post by placing it near the furniture they tend to scratch and rewarding them when they use it. Regularly trim your cat's nails and use a nail file to keep them smooth, which can reduce their desire to scratch furniture.
It is unlikely your older neutered cat has suddenly developed the urge to spray urine everywhere to mark his territory, unless another uncastrated tom has wandered into the area and is marking the territory. I would suspect your cat has a urinary problem and that he is not able to make it to the litter box in time. You should talk with your vet about this, and about what cleaning products are available to get the smell of cat urine out of the furniture.
your cat might be old.
One cat may suddenly start hissing at another cat due to territorial behavior, fear, or feeling threatened. It could also be a sign of aggression or discomfort in their environment.
For cat scratches you can use a furniture marker to cover up any blemishes.