I used Aspen mixed with spring water (just a drop) a couple times a day for a week(Edward Bach Remedy)to help on that situation.It relaxes their muscles.
Or get feliway plug-ins.
Or calms from revivalanimal.com it works like feliway.
My Tucker and Jasmine were rivals bigtime until recenty.
Now....I accually saw them huddled together under the bed when the guy came yesterday to fix the furnace.And they were calm next to each other.Me and Mike just looked at each other with our mouths open in shock.But I did notice no more tifs the past few days.Everything is so quiet...it's almost scary
I ended up buying the whole collection a while back and the book on how to administer them.
The book is called:
Bach Remedies for Animals by Helen Graham and Gregory Vlamis
This paricular book is accually the easyiest reading for learning on how to administer them.
The behaviorist for animals I went to told me about this book.
good luck