I've had many cats over the years. Follow the ideas you are reading here. But, I also give both the new cat and the old cat equal affection. Also, with the older cat I talk to the older cat while I am grooming her. I may tell her that we have a new friend living us. And that will take awhile for us to get used to each other. Show them both lots of love and affection. Animals are very receptive to love. Give them both floodtides of love.