I think you are getting lots of good advice here. I'm chiming in because I've done cat rescue quite a bit.
I have seen lots of people who were happy with TOTW foods. I think they are a high quality cat food. But all animals do better on different foods. I have seen cats and dogs that did better on cheaper/more expensive foods that did not seem to make particular sense. I think that they each are unique.
If all this started when you changed food, I would change back and see if it goes away. Some times it has to do with the PH of the food, and the cat develops urinary crystals from having urine that isn't the correct PH. So food can be prescribed that brings the PH back in balance. I would be hoping that this isn't the problem because it tends to be lifelong.
The one you are pretty sure is peeing in the house, I'd take that one to the vet and get it checked out. Lots of times cats pee inappropriately because they have a urinary issue, especially when a housetrained cat begins doing this and no new cats have been introduced to the household. Urinary tract infections are famous for making cats pee all over. Try giving them extra water or water from a cat fountain which encourages them to drink more. Cats that pee right in front of you especially tend to be the ones with a urinary health issue.
I would try "cat attract" litter. Cat pheremones can help (you can get them at Petsmart). The ladies in the cat rescue that I volunteered with all thought "Max Cat" encouraged urinary health.
I would put a litter box in that upstairs area where the dogs are, but use a dog proof one. There are some you can buy ready made or you can make them like I do......from a big cat box sized rubbermate tote. You cut a cat-sized hole in top and they learn to sneak through the hole (make the hole too small for your dog to fit through). If you have a chihuahua, it probably is small enough to fit through, but make the hole in the TOP of the tote and it would be awkward for him to make it in and out. My cats don't know what a normal litter box looks like, I have five dogs.
I would also try to isolate as Metal suggested, it is hard to sort things out if you don't know who is for sure making the mistakes. And sometimes cats do better if their litter box and territory is individual.
I hope my advice is helpful.