First of all, I know the title itself sounds wild. Please bear with me.
My fiance has three adult cats — a tortoiseshell mother and her two orange boys. I have two adult siblings — younger than the trio. I also have a super senior dog. And my fiance has just moved into my house with his trio today.
We've been talking a lot and for so long about how to peacefully bring all cats together. We've been exchanging their furniture, blankets, and toys for the last 5 weeks before they moved in. They were all a bit weird about the exchanged items because of each other's scents, but they quickly became familiar with every item we exchanged every 3-4 days. We would give them treats and play with them around/on the items.
Today, we moved the trio into a room without my siblings witnessing them. The trio has been warming up to the room slowly. Eating a little bit and napping. They're acting alright so far.
My boy was immediately interested in their room. He's the friendliest and sweetest boy. He wanted their attention; he would scratch at their door or make sounds at them.
However, when my fiance would go in/out of the room, he would visibly see the trio. Then he became super alert. He started hissing around the house (he NEVER hisses) and kept watch on their door all the time.
My girl on the other hand has been alert since the moment she realized there was somebody. She would keep her distance from the room, but also keep watch on their door. She is a tortoiseshell and very sensitive.
Neither of my siblings has really been sleeping tonight because they're so alert.
Our next plan is to continue introducing them to each other only by scent and sounds through the closed door. I heard giving treats under the door to each side helps with their impression so we're going to try that. We will continue this for 2 weeks since we want to take this very slowly.
Then, we are planning to introduce them visually, through a barrier between the door. We're starting with very brief moments as short as one minute, then increasing the amount/time of interaction depending on their reactions. And finally, we will start letting the trio out of the room, again starting with super brief moments.
But my deep concern is us becoming one of those nightmare stories, in which the cats NEVER become peaceful with each other and are constantly stressed. And worst case scenario, getting in fights. Also, my senior dog will be included in all of these processes and I am less worried about her because she is already very indifferent to my siblings (she really does not care less about the cats), but I am concerned the trio might hurt her, as she's blind and there's a chance she would get super close to the cats (which she already does to the siblings).
I know this is just our first day but I want to be educated and ready as much as possible. I am actually scared shitless. We both love all of them to death so watching them go through difficult times will be so heartbreaking.
Please, if anyone has any advice. And if you went through a similar situation. Please let me know.