We have a 3 year old female cat. We have had her for a year and a half. She is laid back, affectionate.. We just love her. Today we brought home 2 kittens. They are rescues. They are 1 1/2 months. They keep hissing at our cat and she is scared. I think they might be scared, too? The first few hours they were here, everything was fine. Until all 3 found themselves in the same hallway at the same time. Any advice, please? The lady said if they don't get along with our cat, we can bring them back. I would like to try to make it work. Thanks.