You want advice??? here it is.....TIME

The cats need to work it out, and they will. My little Kim, all 4 pounds of her, growled and hissed at everyone. (and they are all 2 to 3 times larger) for quite a while. As did Sterling and Biddy and Monte and Jasper............. etc. when they were the new cat trying to adjust.

Try to ignore their attitude but at the same time give them love. It will work out.