I am not sure how much this will help you (as you don't know how long this has been going on) but, what I did when I found a pee stain on my parent's (gasp) leather coach cushion was the following:
1. Remove leather cover from cushion and put both in a room the cats could not get to.
2. Use metal cookie sheets, pillows, etc. to cover the rest of the coach seats.
3. Spray the foam cushion thuroughly (until very wet) with nature's miracle just for cats...Do this only in the spots that smell and the surrounding areas.
4. Dab the top of the cushion with a cloth and let dry (put in a room with a fan to circulate the air).
5. I flattened out the leather seat cover with a towel inside to prevent the moisture from going into the bottom of the cover. Isolate the spots on the leather that smell (i.e. I had to sniff the entire cover with my nose ~ 1/2" above the leather). Spray that area of the cover 1 time with nature's miracle and dab quickly and thuroughly with a dry washcloth... You don't want to leave the leather wet, just damp.
6. Let seat cover and cushion dry for ~ 15-20 minutes then repeat, repeat, repeat... I did this for about 1 whole day with the leather seat cover and 2 days with the foam...with the foam, I had to get it sopping wet because the NM has to soak down to where the pee stain is or the odor won't come out.
7. Keep the cats away from the items while they dry!! NM recs up to 2 weeks for something to fully dry and for the odor to be completely gone...I let the foam cushion dry outside for ~ 5 days before I put the leather cover back on it. When I did put it back on it, I kept metal cookie sheets over that seat of the couch for 1 week to keep the cats off.
This worked for me (thank goodness as my parents would have killed me) but I think it worked because I caught the stain the same day (thank God that I stayed home sick from work that day and found it). I think that the most important thing is getting rid of the odor as completely as you can...otherwise the cats will return to pee on the same spot. I don't think the chemicals that professional cleaners use will help with the pee smell (at least the miniscule amount the cats can smell).
Another point, is that the NM or any other cleaners MAY discolor your couch, BUT I'd rather have a slightly discolored couch than a pee-smelling one. I was lucky in that my parents couch is a "distressed" finish olive green color, so the area where it darkened slightly due to the NM isn't noticable. The NM bottle recs trying a small spot first to see what will happen.
In your case, if it is the seat cushion only (like mine) I'd rec reapplying the cleaner multiple times and leaving it in an area with good air circulation (i.e. ceiling fan, not fan pointed at the items drying). Just keep applying and applying until there is no detectable odor w/ your nose right on the spots, then apply some more
I'd check all of the cushions carefully (w/ nose on them) to see if there are other spots. Other than that, make the couch highly undesirable for them to pee on...I'd use cooke sheets w/ like tinfoil or plastic wrap in them (so that if they do pee, it will stay in the cookie sheets...plus you can easily move the sheets if you want to sit and put back when you are out of the room. I'd check the sides/back of the couch too (w/ nose again) and if you are remotely concered about them peeing there, you may want to put plastic wrap or tin foil hanging down.
Good luck, I know how stressful this can be.... and no, I didn't smell my stain either...I noticed that the blanket and cushion on the spot were wet and found the stain underneath (I had a cat w/ a UTI issue).