Hey there. I’ve had this problem a few times throughout my cat owning years.
There are a number of ways to get cat urine smell out as I’ve tried everything and researched it a lot as well. You can start out by gently rubbing it down (depending on the fabric or material the couch is made of) with either a water mixture with vinegar or baking soda or even some good soap and water. But this alone will not completely remove the odor but will start off by trying to remove some of the source and neutralize it. VERY IMPORTANT **** Do not use any bleach or anything that has bleach in it as bleach and ammonia ,which is in urine, mixed together will create toxic gases called chloramines that can lead to nausea, coughing and even can be fatal if inhaled. Then to try to remove the odor itself entirely, there is a cleaner specifically for animal urine called Nature’s Miracle which you can find at almost any big box stores like Walmart or pet stores like PetsMart, relatively cheaply, that you can spray or rub with a cloth into the source that will work miracles. It has directions on the bottle that you can also follow. Or if it’s not available or choose not to use it, you can simply use something like Febreze or a disinfectant spray like Lysol or something similar , as Febreze actually traps and removes like 99% of odors without having to rub it in. Just spray a generous amount and you should be set. Or like I mentioned, a disinfectant spray will do the same thing.
On the issue of the cat urinating on the couch and plant, there are a number of reasons. Sometimes it can be because it’s not feeling well. Sometimes when cats are ill, since they cannot actually tell us verbally, they will act out by urinating on and in places that they shouldn’t to kind of tell us in their own way, but don’t worry as this is not always the case, and even if it is, it usually isn’t serious and can be fixed somewhat easily. It could be a uti or something similar as cats are notoriously bad at drinking water. They just don’t drink as much as they should. Most cats will get sick at some point in their life due to this, causing kidney problems, bladder or urinary tract infections. One of my cats, years ago, even got kidney stones. I currently have a cat with a uti that just refuses to drink water, so I am having to syringe water into her mouth carefully and slowly, making sure not to aspirate her but to try to clear it up. They love the sound of running water, so I bought a small kitty fountain that my other 2 cats absolutely love and it has influenced them to drink more water. A cat, by general rule, needs 1 oz per pound of water daily, so a average 8lb cat needs just about 8oz daily. This can also be achieved by using wet food as it is more than 50% water, so it kind of sneaks the water into them

.... lol.
Not knowing if the cats are male or female or if they’ve been neutered or spayed, sometimes they also may spray when they go into heat or males when they haven’t been neutered to “mark“ their territory. It’s nothing serious, but it’s sure a mess to deal with. On the subject of urinating on the plants, my cats do this often for the simple fact that they just enjoy using it as their cat box because of the dirt, like they’re outside lol.
If you’re financially able to, it wouldn’t hurt to take them for a vet visit just to make sure everything is ok with their health. Other than all of this, let me know if I can help you with anything else. I basically have a cat Wikipedia built into my head at this point, from vast experience and research lol

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