How can I let my new kitten get along with my older cat?
Put the newcomer in a room with the door closed. This way, both of the cats can get to know each other because what they’ll do is play footies with each other underneath the door. They can get used to each other’s scent this way. Or put the new kitty in a cat carrier and let them go nose to nose that way. Only when you’re sure they’ll get along is when you can leave them alone together. Otherwise, the older cat could attack the kitten. The older cat is the one who should have the run of the house since it’s his “territory”. He feels threatened right now because another cat is invading his territory. More than likely, they will eventually get along, it just takes time. This is the way I did it with my cats and it took a few days of having to keep the new cat in a room by herself but it did work.