Wanted to share a home recipe for removing cat urine smell-----it really works. I have tired several of those you buy and those are just scents that cover up and when gone well there remains the smell.
http://www.catsofaustralia.com/urinestainremoval.htm
Some cats will never get along with other cats no matter what you do. Should that be the case the only answer is separation. My daughter who is a Vet has 11 house cats (vets seem to just be everyone's drop off for unwanted) and she has her 2 old lady cats she calls them that have to stay in a room away from the rest. They do get along well together though. One for a long time would just climb up on the mantel and not get off so she finally just gave in and gave her private room and the other one she added later.