Two cats one of them is using my couch for a cat box which one and the other issue is that one is also deaf.

You may need to get a separate cat box for each cat.

When you catch the cat going on the couch, pick them up and put them in the cat box. Clean the couch and use vinegar to get rid of the smell. It'll take awhile, but it's just something you have to work at.

Try Nature's Miracle to clean the couch. If there's any smell (and remember they'll smell what you don't), they could keep using it.

Are you providing a box? Cats will naturally tend towards the litter box, so there has to be a reason they used the couch to begin with, and you want to be knowing what that reason was. If you've provided no box, then the answer is duh. If the box is there, keep it clean, every day. One for each cat is a good idea. Is it easily accessible? Do they hate the litter?

If it's not a question of the box, then it's something else behavioral, or a medical problem. Behavioral can mean marking territory. (That does not have to mean a male spraying. Females can do this as well.) One might do this if they don't like the other one in that location or something. A medical problem would have to be checked by a vet.

As for a deaf cat, it's not like you can do anything about it. White cats tend towards deafness. Just be careful to keep that one out of harm's way. It can't hear things coming, etc.

A deaf cat will also be more likely to attack if startled. That means, making sure it can SEE you before trying to pet it and trying not to come up on it from behind.

It also means that yelling 'no' will not work as discipline. A squirt bottle will be your best option.

This is sort of the same, I have a deaf ferret, and trying to litter train him was near impossible. I couldn't say no when he pooped on the carpet. I used a squirt bottle first, but then realized he LOVED to be sprayed, I hear some cats do to. When your cat pee's/poops on the couch walk up in front of it, and put your finger in it's face (Like saying no) and then pick it up and place it in it's litter. My ferret learned very quickly if I placed my finger in it's face it was in trouble, and lays there and pouts (it's kind of cute).