One thing I've learnt with cats is that if you appear to be distressed by aspects of their behaviour, this makes their behaviour even worse.
When mine start fighting (real fighting) I used to get into a terrible state, splitting them up and causing the problem to last for sometimes days, however now I do almost nothing, other than keeping an eye on them. They become less agitated and just stop fighting. Now they very rarely fight, but when they do, its over before its started.
I can imagine what you do when Kiwi starts attacking your other cats. Probably what I used to do too. Your cats will see you getting into a state, they will become more agitated, Kiwi will continue attacking, whilst the attacked cats will become more agitated about being attacked. So next time, just don't do anything, and see what happens.
By the way, I think you're aging cats the way people age dogs, ie. 1 dog year = 7 human years. In fact, the 1st year of a cat's life is equivalent to 15 human years, then each future year = 5 human years.
If I'm right, that makes the cats you mentioned 30 and 50 respectively. Not much difference, but over time you'd be aging them too much.
PS. If you find a way of stopping her jumping on the kitchen counter, let me know!