introducing new cat to old cat?

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i have had my cat (coo joo) for about 10 years, we adopted him when he was a kitten at 6 weeks, he was neutered before we took him home. my sister found her cat(kitten) one day when it followed her home, it was a mess and she basically had to rehabilitate it. she is now moving to Hawaii with her husband, the regulations on animals going into Hawaii are very strict and for now, the kitten has to stay in my sisters room which is right next to mine until we can get the cat ready to be shipped to Hawaii. both cats know the other is there and im afraid letting them roam the house together is a bad idea. coo joo has always been aggressive and im afraid the introduction of a new cat(which is a female that hasn't been spayed) will cause more aggression and possibly fighting between the two. both cats need attention and im only one person with lots of obligations. any ideas??