Just brought home a new baby brother for my 3.5 year old adopted at 10 months cat, Autumn. I wanted to give her a sibling she can play with. I got both cats from the same adoption shelter. Autumn is very hesitant and hisses at Dewey but seems pretty tolerant already with this photo taken only a few hours after bringing him home. Dewey got up there all by himself and very much wants to play with Autumn. With some more time and introduction therapy I have a feeling she'll come around pretty quickly.
Yea I'm afraid autumn won't be accepting but I've taken the steps to help that.
Second litter box for Dewey Separate water and food bowl He's staying in my room separately during the night/ part of the day when I'm not home. A separate bed and blanket that's his only and Autumn has her own bed.