Help :( Bad, bad cat(s). At wit's end.

Argh I just typed this entire post and then lost it. Hopefully this time it'll make it through.
   
We have 2 terribly misbehaving cats and have said we can only deal for another month. We don’t know what we’ll do if we can’t turn them around, but I feel as though we’ve tried everything and am hoping you will have some advice for us!!! Here are the details:
   
- two 11-month cats; male & female; siblings. Appear to get along. Sometimes he picks on her a bit, but her tail wags the entire time, so I think they’re fine.
   
- well-behaved for first 3-4 months; have been peeing and pooing all over the basement carpet for the past 8-9 months
   
- the house was brand-new; no previous pets to create odors/scents. No other pets. No kids.
   
- nothing significant changed in our lifestyle or their boxes when the ‘bad behavior’ began
   
- when I began noticing they were peeing on the basement carpet, I used feliway spray and added a 2nd litter box to the basement, which seemed to help.
   
- they haven’t peed or poo’ed anywhere else in the home, and it’s a large home, 3 stories. (Why the basement!?)
   
- they have 4 litter boxes. Last week we removed the lids to the two boxes in the basement, but this still hasn’t stopped the bad behavior. For the past several months they haven’t used the other two litter boxes (main floor & upper level). They primarily use the basement boxes (or the basement carpet.)
   
- not sure which of them is doing it. (or both?) We saw the girl cat pee on the carpet once several months ago…
   
- I have cleaned the carpet numerous times - most recently spending over 12 hours thoroughly cleaning as follows:
   
---- cleaned perimeter of the room (which is where they pee -- it’s everywhere) using Hoover Steam Cleaner and Hoover cleaner for pets. Pre-soaked areas where I could smell pee, which quite honestly was almost everywhere. Let this dry for a week.
   
---- The following weekend I used Nature’s Miracle Just for Cats - soaked the entire perimeter of the basement (super expensive!)
   
---- Once it dried (a few days later), I *covered* it in baking soda
   
---- Took the lids off the 2 litter boxes in the basement
   
---- Plugged in 2 Feliway Room Dispensers/Plug-Ins AND sprayed the Feliway spray in the areas where they tend to go the most. ($$$!)
   
AND THEY ARE STILL PEEING AND POOING!
   
In fact, tonight I was down there scrubbing away and putting down more baking soda, and I watched both of them use their litter box to pee, and one of them pooed in it. (Yay!) Yet moments later I found fresh pee on the carpet!
   
- Their pee is not pink or red, so I don’t think it’s UTI. ?
   
- I’ve tried multiple litters. Right now I’m using Fresh Step Clumping Litter in some boxes and Arm & Hammer in others. Today I added some Tidy Cat Crystals to their downstairs boxes (2) in the hopes of transitioning them to this new litter. I hadn’t tried Crystals before this, so I’m hoping…
   
- They eat Purina Kitten food (dry) and 1x per week Friskies wet food.
   
- They seem happy and sweet. No other ‘bad behaviors’ to speak of!
   
- I’ve tried using a black light to make sure I’m finding every single spot, but the black light doesn’t seem to work on my light shag carpet. So instead I get down and use my nose. Not being sure of exactly where they’ve gone, I’ve fully cleaned the entire perimeter of that basement - dousing it with ‘Nature’s Miracle just for cats’ when I felt I had sucked up every possible ounce of pee - and yet they are still defecating all over the places I’ve cleaned.
   
- The basement STINKS! I’m so sad - this was a new home! That basement is sick and the entire room is unusable. It seemed to smell better after I used the Nature’s Miracle, but with the litter boxes being down there (without lids) and their many secret ‘incidents’, the room once again smells awful.
   
Please help us. We’re animal lovers and can’t bear the thought of getting rid of these cats, but I can’t figure out what to do! It seems that we’ve tried so many things that others have suggested! If you have any advice, please please share!
   

Boxes with lids are no good since they keep the stink of their business confined (think of an outhouse---gross). Also how often are you cleaning the boxes? You should clean them in the morning & the night and use an UNSCENTED clumping litter. Sometimes they will not like the perfumes and go elsewhere. Same goes for the cleanliness. Cats are like people, if their toilet is nasty, they will find another place to go. Since they are going so much on the carpet in the basement, they will return to that area since it smells like the bathroom. You will need to use an enzematic cleaner to completely remove the odor (even if you can't smell it, the cats still can). I'm not sure how much of this you will need...it may be better to pull out the carpet and tile possibly? Also FYI, when a cat wags her tail it does not mean she is happy. It means that she is conflicted or agitated or getting pissed off! She was probabaly getting mad at her brother. She may have been ambushed while trying to go to the bathroom by her brother and now she associates the box with "bad things" so she avoids it. Could be a reason. Good luck, just keep trying things. There is always a reason why cats do what they do, you will have to play detective.

One more thought...the Feliway mainly works for anxiety or territorial peeing. This does not seem to be your issue (territorial peeing is found on vertical surfaces (spraying) not horizontal surfaces). The Feliway is supposed to calm cats and sooth them, they probably find the basement inviting because of the Feliway...and the pee smell further invites them to use the carpet to go to the bathroom.