[Purple-Hops]

Hmm, I can't be too sure.. Honestly I would introduce them ALL at the same time. There's no telling how territorial one pair would be if they got there first. Pet stores and vets carry this stuff called Feliway. (And other brands I'm sure) which is a happy cat pheremone developed to relive stress on cats. Here's the link.. Good luck!! Also, welcome to the forum
http://www.feliway.com/us