I’ve had a kitten for almost 2 months and have adopted a friends older cat. My kitten tries to be friendly but the adult cat hisses and tries to attack. I have put them in separate rooms with the doors between them slightly open and each has their own food, water and litter box. Should they get along better over time? I feel sorry for the older cat because she seems stressed out and won’t leave her hiding spot, even though the kitten is being friendly.