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Hi. My name is***** Thank you for your question. This is a situation where the unknown is there. Some cats can start marking / spraying as they are in a new environment. Typically these are male cats that do this. The other unknown is the resident cats themselves may start to urinate inappropriately in the house with the other cat being inside now. Some when stressed can start to urinate inappropriately. It is great that they are getting along as that may mean peace is at and and there will be no marking or inappropriate urination. Time will tell though. The best you can do for them is to make sure they have easy access to litter boxes and make sure they are cleaned more regularly to make them as pleasant as possible.