Dear MazieD, the fun starts when you introduce two females to each other, especially if yours love your DH and regards him as her property!
Introducing two male cats to each other is a doddle in comparison - they behave like boys in a school playground, once they have fought each other, they become the best of friends.
Remember how long it took a new girl to fit into a class in junior school? Cats behave the same way.
Washing bio gel or quid in the drum