I have three cats, one is almost two years and the other two are a little over a year. The two youngest ones are my girls and when we got them they were very young but already potty trained. For the most part they always use the litter box but they also have been pooping in the stairwell and wetting either on the couch or bed. We have reason to believe it is both of them but we dont know what the issue is. If they know how to use the litter box why aren't they using it all the time?? In desperate need of assistance other wise we may need to find them new homes. I need to be able to use my bed and couch again without it being covered in cat urine.

There are various possibilities -- it may only be one of your cats doing this.

One cat may have a urine infection -- have you observed one cat urinating in the litter box in small quantities frequently? Or sitting in the litter box but not passing anything?

Are your cats all indoor only cats? If so, you need 3 litter boxes, though 4 is better (one for each cat plus an extra box). Or do they all have outdoor access 24/7 ? Some cats are very fastidious and will not use a litter box that's been used by another cat. Also, cat litter can become smelly even when you are taking out the used stuff constantly. A very fastidious cat with a sensitive nose will object to using a box that smells of other cats to them.

Might be a territorial issue -- how long have you had the 2 young females? Could it be one of the cats (even the older cat) is feeling insecure about their territory. May be necessary to create some places where they can get away from each other e.g. perches around the house.

I suggest you deny them all access to your bedroom until you have resolved the problem. And only allow them to have supervised access to the sitting room, to stop them using the couch as a toilet.
As for the stairwell, you could try feeding one of them there regularly so they begin to associate that part of the house with eating not toiletting.

I still have problems with my younger cat Snoopy.

Snoopy always does it in corners we have put litter trays around the areas that she likes to do it.

Make sure that you clean your bed and settees with proper cleaning equipment to ensure the smell has gone.

You could try the spray or plug in stress relievers from the vets they work for some cats unfortunately not mine.

Have you noticed any blood in the urine it could be a urine infection or cystitis, which is common in female cats if so the vets can give you something to help.

Good Luck if you ever find a solution please let me know