I think we're making progress! Hannah & Canute have been off the clomacalm pills all week (still don't think they did anything - although vet says primarily he sees them effective for inappropriate peeing). It's pretty funny to see Canute & Henry very carefully, quietly slink around Hannah - trying not to be noticed! She usually does anyway, but now she's just lightly growling. Many times Canute just sits a few feet away and stays there. There has been a definite decrease in the number of screaming hissy fits that have to be broken up! She's not really mixing in, but at least the fights are less. So maybe by the end of the year, they'll have learned to tolerate each other. Just in time to screw everyone up with the move!!
So wish she'd accept them like she does Magnus: I saw her & Magnus nose to nose when I went downstairs for breakfast.
So for those of you going through this, it can happen, sometimes. but it may also take 7 months or more. <sigh>