New Cat With 2 Other Cats - How to make them get along!?

Hey there,

So it's been a while since I've needed help with Spike but it's come for that time again. I just went to visit my sister for christmas with Spike, and she already has two cats (Versache - around 15weeks old and Kenzo is less than a year old). So my sisters cats have gotten along great until today when I came here with Spike. Now none of the cats are getting along, Spike is locked in the livingroom afraid to go out, Kenzo in the bedroom the same and Versache in the kitchen. I thought they would team up against Spike but they've left him alone and are attacking eachothet (especially Versache hissing Kenzo, he goes to her and wants to play but she doesn't let him near her)

We're really lost and in need of serious help. I'm going to be here with Spike for a week and we'd love it for them to get along, they don't have to play with eachother or anything just be aloud to move around the apartment, go to the bathroom & eat without being afraid to leave their 'safe-rooms'.

If anyone has suggestions to how to get them to be "ok" with eachothers prescence we'd be forever greatful. And an aswer asap would be so helpful as we're so worried and just lost!

Thanks for your time,

Have you tried Feliway? Vanilla?

Realistically, they probably won't get along within a week.