How to introduce a new cat to the household if you already have cats?
Confine the new cat to a single room. Make sure the confined cat have access to everything he or she needs, including water, food, bedding, litterbox and toys. Feed your new and existing cats across the closed door, so that the cats can smell each other and associate each other's presence with food and happiness. Use synthetic feline facial pheromone in both the new cat’s room and in the area where the resident cat spends the most time will help to create feelings of familiarity and security within the physical environment. After a while, exchange pieces of bedding between the resident cats and the new cat so that the cats start to recognize each others scents. Slowly allow cats to interact with each other under supervision to ensure the cats build early positive experiences together.