First, know that your other pets have staked a claim on your home, and need to be reassured that the newcomer isn’t there to oust them. By keeping your kitten in the “safe room,” your other pets will already be aware that he or she is there. They have already had an opportunity to get used to their scent. When the first meeting takes place, keep it short. Let them all get the chance to see what that odd scent in the “safe room” was, but don’t let your kitten become too frightened or your other pets too aggressive.
From then on, allow the pets to be in the same room together, with supervision, until they’ve all become used to each other. They will work out their issues, given time. This could take a week or more, but exercise patience and be sure to lavish attention and reassurance on your established pets, to stop any jealousy in its tracks. If at any time you feel like the new kitten is in danger, put him or her back in the safe room and keep trying. Using “NO” in a loud voice or squirting a water bottle at a dog that chases your kitten, will eventually train them to leave the kitten alone.