My cat is spraying in the floor vents!

Question:
 I need advice!  I have a 2 year old male cat that I have raised since he was 3 weeks old.  He was neutered and declawed around 6 months of age.  I recently adopted another male kitten that was 3 months old at the time I found him.  The 2 of them fight something fierce!  The kitten does provoke the older cat.  However, the older cat has recently started going to the floor vents (for my heating and air conditioning) and spraying in the vents.  He has done this in every room in the downstairs area of the house.  When the heat kicks on, you can imagine the terrible odor that permeates throughout the house! How do I stop this bad behavior?  I do not want to find the older cat another home but I can not tolerate this beavior.  I also need to mention that I have another male cat that is 10 years old.  He does not fight with the other 2 cats and does not seem to be a part of the problem.  HELP!
Answer:
 Hi, I will try to help with advice. The male that is spraying, you have had him since 3 weeks of age; & he has been sole pet in the house, I assume. Bringing in the kitten, without telling him (as silly as that sounds) that he would have a new friend. He possibly feels hurt (animals do feel emotion as well as humans) that you felt he was not enough companionship/friend for you. Also, a new pet should be slowly introduced into the house/apt. Where you would have the new pet in a small to medium dog crate or cat cage (not carrier); & while you are in the room, supervise the meetings, as it were, between the older cat & the kitten. It has always been a practice (for this family) to slowly introduce new pets into the household. We use a medium dog crate, where we place litter pan, food & water bowls which hang on inside of cage, and a cushy blanket for cat to sleep on. Then let the other pets walk up to the cage, get acquainted with the new member of the household, etc. Most important, always give the other pet(s) equal attention & play time; as with the new arrival. And let the other pet(s) know that they are not being replaced, you still love them & assure them of this everyday. As for the older cat spraying, even though he is neutered. He is retaliating against you, "punishing" you in his way, letting you know that he does not appreciate the new member of what he considers his family. I would suggest purchasing a cat cage (not carrier) or a small to medium dog crate, place the kitten in there while you are not home or asleep, etc. Only let the kitten out, while you are there to supervise. If the kitten provokes the older cat, squirt the kitten with a water bottle, which you should always have on hand, & tell it no at the same time. Scoop the kitten up & put him/her back in the cage. If the older cat provokes the attack, squirt him with the water, telling him no & put him in his cage, which he should also have. It might come down to you having to purchase "kitty-diapers" or "small dog diapers" to have the cat wear; until the spraying & jealousy stops; but this means always having to follow him whenever he needs to use the litter box. I am sorry for the novel, but I was trying to think of suggestions for your situation. I hope this helps. Aquila
Answer:
 As he is a male he could be marking his area. This could be because of the other cat. Also, i do very much agree that they are stressed with such a small area. You could make the cats bond more or maybe consider if the cat means alot to you] moving to a slightly bigger place.