Two years ago my cat and I moved from a 3 cat household to a one (my cat Luna) household. Luna was one happy cat and I was her hero. Her paradise only lasted 1 year.
Max needed a home and he came to stay. She didn't mind him too much, he was older, 6 to her 7, and he was a gentleman. He didn't eat her food, nap in her bed, didn't take up any of her walking/grooming time, and every now and then he consented to play. She could live with him.
Six months after Max, her peaceful, comfortable way of life came to a screeching halt. Tiger became her new little brother. Tiger was 8 months old. He demanded attention from everyone. He jumped on everything and everyone, including dogs and other cats. He stole her food, slept in her favourite place and just generally sent her life into an upheaval. Sadly for Luna, Tiger is here to stay.
I have tried to make sure Luna does not feel displaced by Tiger. She is, after all, my #1 girl, and will always have first place in my heart. These are a few of the things I have done to ease her transition from only cat to cat with a bratty little brother.
1. Keep Her Sleeping Place Sacrosanct
Luna's bed is for her alone. Her sleeping place is not the same as her napping place. She tends to use different areas of the house for naps, as do the other cats. Those places are for whoever gets there first. Her bed is where she spends the night and no one else gets to take that place.
2. Luna Gets Her Food First
The 3 cats get both wet and dry food. They all eat at the same time, in the same area. In the morning and evening when I divide up the wet food between the 3 of them, Luna has her dish put in front of her first, then the other two get theirs. Because Tiger still gulps down his food as fast as possible and then tries to eat from the other cat's plate, I stay in the room to stop him stealing their food.
3. Luna's Routines Stay the Same
Cats have rituals, at least mine do. Every evening before bed, Luna would get groomed. Every morning after eating, Luna went for a walk. Sometimes, with Tiger flying around the room playing attack cat, it wasn't easy but we stuck to our grooming schedule. For her, the walk is the most important, not only is it about getting outside where there is grass to eat and things to see, but it is away from Tiger.
Eventually Tiger is going to calm down, he already has to some extent, and he will stop jumping on her, chasing her and nipping her bum, and she will learn to like him. I hope.
My blog about my cats: http://beautifulfelines.blogspot.com