Only 7 here at the moment
, but have lived with a 13 multi household and yes, with the right introductions they can work. I use Feliway at stressful times i.e. when I'm having a new arrival, or if I have foster cats in the house.
Plug in Feliway a week or so before newbie arrives and leave in place for maybe a month, new cat has own room initially, until newbie and residents have got used to the scents and sounds of each other, then face to face meetings under strict supervision to begin with, separate again at night, until such times as I feel they are safely (and happily) integratinging - that can be as little as a week in some cases, and months in other cases.