I am sorry that you have been waiting for a response. I recently just logged onto the site and noted that your question hasn't yet been answered. I am a licensed veterinarian with over 25 years’ experience and would be happy to work with you if you are still needing assistance.
Bless you for taking this guy in and I am sure it is stressful for all. It is very possible all of his urinary tract signs are due to the stress of the move and the new environment, and I am going to discuss with you what you can do to possibly help that situation, but if it is not improving, unfortunately you will need to seek veterinary intervention to rule out other causes. . Cats can be affected by a condition called Feline Lower Urinary Tract Disease (FLUTD) which is the name given to a set of symptoms from various causes that can affect a cat's urinary system. The causes are varied and the age of the cat partly influences the likelihood of the cause. (ie older cats are more prone to bacterial infections than younger cats). Other common causes include bladder stones, crystals, tumors, and sometimes just inflammation from an unknown cause (more common in younger cats). Unfortunately, the all can show the same symptoms, no matter the cause and all are treated a little differently. This inflammation from that occurs due to unknown cause is referred to as feline idiopathic cystitis (FIC) and it is very likely that is what Zorro is experiencing as it is a condition that is definitely shown to be precipitated by stress. Here is an link to more information about FIC in cats. LINK HERE The good news is that many of these cats will improve on their own regardless of what treatment we provide. Usually we try to give them something for their discomfort until it resolves and make sure they don't obstruct. It is not uncommon for their symptoms to return again later and can come and go periodically throughout their life. In the short term, the very first thing that you can do is to increase his water intake. You can do this by adding warm water or broth to his food. If he is not eating a canned food, I would try to transition him over to that. I would stop with the apple cider vinegar as that will only serve to acidify his urine which can make him more likely to form crystals. Next you need to work on decreasing the stress all around.
I am not sure if you have been confining him or not at this time, but when bringing in a new cat, it is best to give him his "own room" for a short while. From a behavior standpoint, it can be a little less threatening to the other cat(s) in the house if his living space is somewhat restricted to start versus being allowed to have full run of the house right from the start. Cats do not really have a hierarchy in the household, like dogs do, but they are somewhat territorial and may be upset if all of a sudden someone takes over their favorite spot or favorite litterbox.
Even when confining him, the others will know he is there and they will be able to get used to his sounds and smells through the door, before he is allowed to mingle full force. Even when you start letting them mingle, I would do it slowly and only when you are there to observe at first. If they are left all out on their own, there may be altercations that occur that you are not even aware of. Depending on what the set up of your house is like and where the other cats like to hang out, maybe you could alternately confine them in specific areas of the house and let him roam around some also. Eventually, the goal is to allow everyone to be out at all times, but it is often best to build up to that gradually.
Most cats do not like to live with one another right off the bat so we have to strive to provide an environment where all cats are able to find a place where they feel "safe". That begins by creating an environment of "plenty." There should be plenty of litter boxes, food bowls, climbing towers, toys and resting areas in multiple locations. All the litter boxes and food bowls cannot be clumped all in one place because that forces the cats together, something they don't want to do.
One other thing I would suggest is a product called Feliway®. Feliway is a synthetic pheromone that mimics the natural chemicals that a cat secretes. It creates a comforting, reassuring feeling that has a calming effect. It is calming to cats in stressful situations such as transport, hospitalization, veterinarian visits, boarding, new environments, pets or people. Feliway® is a product that can be sprayed or used as a room diffuser. It can be purchased through veterinarians and pet stores. In your case, a few room diffusers may help low the tension. LINK HERE
I am also including a link to a website about environmental enrichment for the cats. The Ohio State University has composed this to help cat owners structure the environment to provide adequate physical and mental stimulation. There are numerous medical conditions in cats that are precipitated by stress and multicat households are often those with more stress, even if not perceived by the humans in the house. Hopefully there are some ideas there that you can incorporate to help keep the stress levels under control
OSU Indoor Pet Initiative
After trying these, if he is still exhibiting the bloody urine or the spraying, he at least needs to have a urinalysis to try to identify any underlying medical problems.
I hope this is helpful. Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please reply so I can clarify for you.
My posted replies are for general education only and not meant as a diagnosis. Only after a thorough veterinary examination can a diagnosis for your pet be made and specific treatments be advised or medications be prescribed.