If people are doing that then they are completely abusing the privilege of understanding a dogs mind. People should seek to understand how a dog's world works and then use that to positively train their dog and build a deeper relationship with him/her, not use it to bend a dog to their will using an iron fist. I would consider what they are doing damaging manipulation. How sad
I can see why that would upset you! I'm sorry that that is such a heated thing and that you've gone through that.
I know Canine Assistance uses pack mentality to positively train their dogs. They say that dogs generally don't long to be alpha, that they have security in knowing that they have a confident and loving leader. A leader perceived as insecure makes a dog then feel insecure and therefore forced to step up. A wonderful leader makes them feel taken care of, knowing that they can trust that person to protect them and provide them with all of their needs. So they teach how to be a confident leader that gives the dog security, and that by showing yourself as such a leader that the dog will long to please that leader. They compared it to a parent/child relationship. That a child feels secure and very loved when they have parents that are leading them and show confidence that they can care for them. Children that feel like they have to be the ones to take care of their parents are often stressed and don't have the most positive relationship with them generally. But a good parent would lovingly guide, not be a mean commander. They taught that you never to hit, yell at, or use force against a dog. This positive training builds a relationship of loving service between dog and human. That is one of my favorite things about dogs. They have such a humble servant attitude and loyalty and I feel that a dog owner is equally obligated to return such. Dogs are such selfless creatures. Ugh now I feel all fired up at those people too
No apology needed, I could see how that subject could get very heated very fast.
A change in litter box can affect it. Sometimes cats will not use a box based off of location, type of litter used, or type of box. I've met cats who won't use a covered box. Have they been defecating outside of the box as well?
As far as separating them I would do it just for a couple of days. It shouldn't take long to see which one it is. I wouldn't separate them until you get them both looked at by the vet though to rule out medical. They may not like it. It is also possible that they might enjoy a break to just be by themselves with all that is going on. Unfortunately I can't predict that. This is only if you want to figure out exactly which one is doing the spraying. I see nothing wrong with just treating the situation like both are spraying and seeking ways to reduce stress in both.
I would try to get a urine sample to take in with you. You can call a vet to see if they would like you to take a urine sample and drop it off or bring the cats in. Chances are they will ask you to bring them in to examine them. I can't give you an answer on how long seeing a vet can wait only because I can't tell you exactly what the issue is. I suspect UTI, but I have no proof whatsoever.
I hope that I've been of help in some way!