Glad to hear you are getting professional help Poblet, vet/behaviourist is the only answer IMO.
In answer to BigBHM, my male cat (neutered, but he was the 'leader') started spraying in the house when we got a male kitten (he had accepted a succession of other kittens during his long life but this was the last straw apparently). I used the correct cleaning processes, and also used Feliway - nothing stopped him. My vet said it is almost impossible to stop once it's become a habit because it's impossible to get rid of every trace of smell, and the only answer is to get rid of the cause of the stress (in my case, the kitten, in your case, lack of space). He was absolutely right, the spraying only stopped when we moved house and they had a massive garden and could avoid each other (fortunately didn't actually have to get rid of the kitten
).
In answer to BigBHM, my male cat (neutered, but he was the 'leader') started spraying in the house when we got a male kitten (he had accepted a succession of other kittens during his long life but this was the last straw apparently). I used the correct cleaning processes, and also used Feliway - nothing stopped him. My vet said it is almost impossible to stop once it's become a habit because it's impossible to get rid of every trace of smell, and the only answer is to get rid of the cause of the stress (in my case, the kitten, in your case, lack of space). He was absolutely right, the spraying only stopped when we moved house and they had a massive garden and could avoid each other (fortunately didn't actually have to get rid of the kitten
).




.